diff --git a/src/effects/desktopgrid/qml/DesktopView.qml b/src/effects/desktopgrid/qml/DesktopView.qml
index b2f93537da..5565cc3c1e 100644
--- a/src/effects/desktopgrid/qml/DesktopView.qml
+++ b/src/effects/desktopgrid/qml/DesktopView.qml
@@ -46,7 +46,7 @@ FocusScope {
     Connections {
         target: effect
         function onItemDroppedOutOfScreen(globalPos, item, screen) {
-            if (screen != targetScreen) {
+            if (screen !== targetScreen) {
                 return;
             }
             const pos = screen.mapFromGlobal(globalPos);
@@ -91,7 +91,7 @@ FocusScope {
 
     WindowHeap {
         id: heap
-        function resetPosition () {
+        function resetPosition() {
             x = 0;
             y = 0;
         }
@@ -113,8 +113,8 @@ FocusScope {
             screenName: targetScreen.name
             clientModel: desktopView.clientModel
             windowType: ~KWinComponents.ClientFilterModel.Dock &
-                    ~KWinComponents.ClientFilterModel.Desktop &
-                    ~KWinComponents.ClientFilterModel.Notification;
+                        ~KWinComponents.ClientFilterModel.Desktop &
+                        ~KWinComponents.ClientFilterModel.Notification
         }
         delegate: WindowHeapDelegate {
             windowHeap: heap
diff --git a/src/effects/desktopgrid/qml/main.qml b/src/effects/desktopgrid/qml/main.qml
index d7af5f2649..e2deb30ab7 100644
--- a/src/effects/desktopgrid/qml/main.qml
+++ b/src/effects/desktopgrid/qml/main.qml
@@ -5,10 +5,10 @@
     SPDX-License-Identifier: GPL-2.0-or-later
 */
 
-import QtQuick 2.12
-import QtQuick.Window 2.12
-import QtQuick.Layouts 1.12
-import QtGraphicalEffects 1.12
+import QtQuick 2.15
+import QtQuick.Layouts 1.15
+import QtQuick.Window 2.15
+import QtGraphicalEffects 1.15
 import org.kde.kwin 3.0 as KWinComponents
 import org.kde.kwin.private.effects 1.0
 import org.kde.plasma.core 2.0 as PlasmaCore
@@ -26,17 +26,17 @@ Rectangle {
     color: "black"
 
     function start() {
-        container.animationEnabled = true;
-        container.organized = true;
+        animationEnabled = true;
+        organized = true;
     }
 
     function stop() {
-        container.organized = false;
+        organized = false;
     }
 
     function switchTo(desktopId) {
         KWinComponents.Workspace.currentDesktop = desktopId;
-        container.effect.deactivate(container.effect.animationDuration);
+        effect.deactivate(effect.animationDuration);
     }
 
     function selectNext(direction) {
@@ -87,19 +87,19 @@ Rectangle {
     }
 
     Keys.onPressed: {
-        if (event.key == Qt.Key_Escape) {
+        if (event.key === Qt.Key_Escape) {
             effect.deactivate(effect.animationDuration);
-        } else if (event.key == Qt.Key_Plus || event.key == Qt.Key_Equal) {
+        } else if (event.key === Qt.Key_Plus || event.key === Qt.Key_Equal) {
             addButton.clicked();
-        } else if (event.key == Qt.Key_Minus) {
+        } else if (event.key === Qt.Key_Minus) {
             removeButton.clicked();
         } else if (event.key >= Qt.Key_F1 && event.key <= Qt.Key_F12) {
             const desktopId = (event.key - Qt.Key_F1) + 1;
             switchTo(desktopId);
         } else if (event.key >= Qt.Key_0 && event.key <= Qt.Key_9) {
-            const desktopId = event.key == Qt.Key_0 ? 10 : (event.key - Qt.Key_0);
+            const desktopId = event.key === Qt.Key_0 ? 10 : (event.key - Qt.Key_0);
             switchTo(desktopId);
-        } else if (event.key == Qt.Key_Up) {
+        } else if (event.key === Qt.Key_Up) {
             event.accepted = selectNext(WindowHeap.Direction.Up);
             if (!event.accepted) {
                 let view = effect.getView(Qt.TopEdge)
@@ -107,7 +107,7 @@ Rectangle {
                     effect.activateView(view)
                 }
             }
-        } else if (event.key == Qt.Key_Down) {
+        } else if (event.key === Qt.Key_Down) {
             event.accepted = selectNext(WindowHeap.Direction.Down);
             if (!event.accepted) {
                 let view = effect.getView(Qt.BottomEdge)
@@ -115,7 +115,7 @@ Rectangle {
                     effect.activateView(view)
                 }
             }
-        } else if (event.key == Qt.Key_Left) {
+        } else if (event.key === Qt.Key_Left) {
             event.accepted = selectNext(WindowHeap.Direction.Left);
             if (!event.accepted) {
                 let view = effect.getView(Qt.LeftEdge)
@@ -123,7 +123,7 @@ Rectangle {
                     effect.activateView(view)
                 }
             }
-        } else if (event.key == Qt.Key_Right) {
+        } else if (event.key === Qt.Key_Right) {
             event.accepted = selectNext(WindowHeap.Direction.Right);
             if (!event.accepted) {
                 let view = effect.getView(Qt.RightEdge)
@@ -131,7 +131,7 @@ Rectangle {
                     effect.activateView(view)
                 }
             }
-        } else if (event.key == Qt.Key_Return || event.key == Qt.Key_Space) {
+        } else if (event.key === Qt.Key_Return || event.key === Qt.Key_Space) {
             for (let i = 0; i < gridRepeater.count; i++) {
                 if (gridRepeater.itemAt(i).focus) {
                     switchTo(gridRepeater.itemAt(i).desktop.x11DesktopNumber)
@@ -154,7 +154,7 @@ Rectangle {
         id: grid
 
         property Item currentItem
-        readonly property real targetScale : 1 / Math.max(rows, columns)
+        readonly property real targetScale: 1 / Math.max(rows, columns)
         property real panelOpacity: 1
 
         Behavior on x {
@@ -199,8 +199,8 @@ Rectangle {
                 when: container.effect.gestureInProgress
                 PropertyChanges {
                     target: grid
-                    x: Math.max(0, container.width / 2 - (width * targetScale) / 2) * container.effect.partialActivationFactor - grid.currentItem.x * (1 - container.effect.partialActivationFactor)
-                    y: Math.max(0, container.height / 2 - (height * targetScale) / 2) * container.effect.partialActivationFactor - grid.currentItem.y * (1 - container.effect.partialActivationFactor)
+                    x: Math.max(0, container.width / 2 - (grid.width * grid.targetScale) / 2) * container.effect.partialActivationFactor - grid.currentItem.x * (1 - container.effect.partialActivationFactor)
+                    y: Math.max(0, container.height / 2 - (grid.height * grid.targetScale) / 2) * container.effect.partialActivationFactor - grid.currentItem.y * (1 - container.effect.partialActivationFactor)
                     scale: 1 - (1 - grid.targetScale) * container.effect.partialActivationFactor
                     panelOpacity: 1 - container.effect.partialActivationFactor
                 }
@@ -213,8 +213,8 @@ Rectangle {
                 when: container.organized
                 PropertyChanges {
                     target: grid
-                    x: Math.max(0, container.width / 2 - (width * targetScale) / 2)
-                    y: Math.max(0, container.height / 2 - (height * targetScale) / 2)
+                    x: Math.max(0, container.width / 2 - (grid.width * grid.targetScale) / 2)
+                    y: Math.max(0, container.height / 2 - (grid.height * grid.targetScale) / 2)
                     scale: grid.targetScale
                     panelOpacity: 0
                 }
diff --git a/src/effects/overview/qml/DesktopBar.qml b/src/effects/overview/qml/DesktopBar.qml
index 7a2fe28af7..e4b6b6ca2f 100644
--- a/src/effects/overview/qml/DesktopBar.qml
+++ b/src/effects/overview/qml/DesktopBar.qml
@@ -4,11 +4,11 @@
     SPDX-License-Identifier: GPL-2.0-or-later
 */
 
-import QtQuick 2.12
-import QtQuick.Controls 2.12
-import QtQuick.Layouts 1.12
-import QtGraphicalEffects 1.12
-import org.kde.kirigami 2.12 as Kirigami
+import QtQuick 2.15
+import QtQuick.Controls 2.15
+import QtQuick.Layouts 1.15
+import QtGraphicalEffects 1.15
+import org.kde.kirigami 2.20 as Kirigami
 import org.kde.kwin 3.0 as KWinComponents
 import org.kde.plasma.components 3.0 as PC3
 import org.kde.plasma.core 2.0 as PlasmaCore
diff --git a/src/effects/overview/qml/DesktopView.qml b/src/effects/overview/qml/DesktopView.qml
index 4ee844844a..0c38e14a44 100644
--- a/src/effects/overview/qml/DesktopView.qml
+++ b/src/effects/overview/qml/DesktopView.qml
@@ -4,7 +4,7 @@
     SPDX-License-Identifier: GPL-2.0-or-later
 */
 
-import QtQuick 2.12
+import QtQuick 2.15
 import org.kde.kwin 3.0 as KWinComponents
 
 Item {
diff --git a/src/effects/overview/qml/ScreenView.qml b/src/effects/overview/qml/ScreenView.qml
index 56a0f9d19d..88b693aa90 100644
--- a/src/effects/overview/qml/ScreenView.qml
+++ b/src/effects/overview/qml/ScreenView.qml
@@ -4,15 +4,15 @@
     SPDX-License-Identifier: GPL-2.0-or-later
 */
 
-import QtQuick 2.12
-import QtGraphicalEffects 1.12
+import QtQuick 2.15
+import QtGraphicalEffects 1.15
+import org.kde.kirigami 2.20 as Kirigami
 import org.kde.kwin 3.0 as KWinComponents
 import org.kde.kwin.private.effects 1.0
 import org.kde.milou 0.3 as Milou
 import org.kde.plasma.components 3.0 as PC3
 import org.kde.plasma.core 2.0 as PlasmaCore
 import org.kde.plasma.extras 2.0 as PlasmaExtras
-import org.kde.kirigami 2.12 as Kirigami
 
 FocusScope {
     id: container
@@ -257,8 +257,8 @@ FocusScope {
                     filter: searchField.text
                     minimizedWindows: !effect.ignoreMinimized
                     windowType: ~KWinComponents.ClientFilterModel.Dock &
-                            ~KWinComponents.ClientFilterModel.Desktop &
-                            ~KWinComponents.ClientFilterModel.Notification
+                                ~KWinComponents.ClientFilterModel.Desktop &
+                                ~KWinComponents.ClientFilterModel.Notification
                 }
                 onActivated: effect.deactivate();
                 delegate: WindowHeapDelegate {
@@ -269,11 +269,11 @@ FocusScope {
                             return targetScale; // leave it alone, so it won't affect transitions before they start
                         }
                         var localPressPosition = activeDragHandler.centroid.scenePressPosition.y - heap.layout.Kirigami.ScenePosition.y;
-                        if (localPressPosition == 0) {
-                            return 0.1
+                        if (localPressPosition === 0) {
+                            return 0.1;
                         } else {
                             var localPosition = activeDragHandler.centroid.scenePosition.y - heap.layout.Kirigami.ScenePosition.y;
-                            return Math.max(0.1, Math.min(localPosition / localPressPosition, 1))
+                            return Math.max(0.1, Math.min(localPosition / localPressPosition, 1));
                         }
                     }
 
diff --git a/src/effects/private/qml/WindowHeap.qml b/src/effects/private/qml/WindowHeap.qml
index 9a706427fe..f9a8fc4222 100644
--- a/src/effects/private/qml/WindowHeap.qml
+++ b/src/effects/private/qml/WindowHeap.qml
@@ -4,9 +4,9 @@
     SPDX-License-Identifier: GPL-2.0-or-later
 */
 
-import QtQuick 2.12
-import QtQuick.Window 2.12
-import org.kde.kirigami 2.12 as Kirigami
+import QtQuick 2.15
+import QtQuick.Window 2.15
+import org.kde.kirigami 2.20 as Kirigami
 import org.kde.kwin 3.0 as KWinComponents
 import org.kde.kwin.private.effects 1.0
 import org.kde.plasma.components 3.0 as PC3
@@ -32,6 +32,7 @@ FocusScope {
     property bool animationEnabled: false
     property bool absolutePositioning: true
     property real padding: 0
+    // Either a string "activeClass" or a list internalIds of clients
     property var showOnly: []
     property string activeClass
 
@@ -125,7 +126,7 @@ FocusScope {
     }
 
     function findNextItem(selectedIndex, direction) {
-        if (selectedIndex == -1) {
+        if (selectedIndex === -1) {
             return findFirstItem();
         }
 
@@ -147,7 +148,7 @@ FocusScope {
                 }
 
                 if (candidateItem.x + candidateItem.width < selectedItem.x + selectedItem.width) {
-                    if (nextIndex == -1) {
+                    if (nextIndex === -1) {
                         nextIndex = candidateIndex;
                     } else {
                         const nextItem = windowsRepeater.itemAt(nextIndex);
@@ -172,11 +173,11 @@ FocusScope {
                 }
 
                 if (selectedItem.x < candidateItem.x) {
-                    if (nextIndex == -1) {
+                    if (nextIndex === -1) {
                         nextIndex = candidateIndex;
                     } else {
                         const nextItem = windowsRepeater.itemAt(nextIndex);
-                        if (nextIndex == -1 || candidateItem.x < nextItem.x) {
+                        if (nextIndex === -1 || candidateItem.x < nextItem.x) {
                             nextIndex = candidateIndex;
                         }
                     }
@@ -197,7 +198,7 @@ FocusScope {
                 }
 
                 if (candidateItem.y + candidateItem.height < selectedItem.y + selectedItem.height) {
-                    if (nextIndex == -1) {
+                    if (nextIndex === -1) {
                         nextIndex = candidateIndex;
                     } else {
                         const nextItem = windowsRepeater.itemAt(nextIndex);
@@ -222,7 +223,7 @@ FocusScope {
                 }
 
                 if (selectedItem.y < candidateItem.y) {
-                    if (nextIndex == -1) {
+                    if (nextIndex === -1) {
                         nextIndex = candidateIndex;
                     } else {
                         const nextItem = windowsRepeater.itemAt(nextIndex);
@@ -239,30 +240,30 @@ FocusScope {
     }
 
     function resetSelected() {
-        heap.selectedIndex = -1;
+        selectedIndex = -1;
     }
 
     function selectNextItem(direction) {
-        const nextIndex = findNextItem(heap.selectedIndex, direction);
-        if (nextIndex != -1) {
-            heap.selectedIndex = nextIndex;
+        const nextIndex = findNextItem(selectedIndex, direction);
+        if (nextIndex !== -1) {
+            selectedIndex = nextIndex;
             return true;
         }
         return false;
     }
 
     function selectLastItem(direction) {
-        let last = heap.selectedIndex;
+        let last = selectedIndex;
         while (true) {
             const next = findNextItem(last, direction);
-            if (next == -1) {
+            if (next === -1) {
                 break;
             } else {
                 last = next;
             }
         }
-        if (last != -1) {
-            heap.selectedIndex = last;
+        if (last !== -1) {
+            selectedIndex = last;
             return true;
         }
         return false;
@@ -301,8 +302,8 @@ FocusScope {
         case Qt.Key_Space:
             handled = true;
             let selectedItem = null;
-            if (heap.selectedIndex != -1) {
-                selectedItem = windowsRepeater.itemAt(heap.selectedIndex);
+            if (selectedIndex !== -1) {
+                selectedItem = windowsRepeater.itemAt(selectedIndex);
             } else {
                 // If the window heap has only one visible window, activate it.
                 for (let i = 0; i < windowsRepeater.count; ++i) {
@@ -319,7 +320,7 @@ FocusScope {
             if (selectedItem) {
                 handled = true;
                 KWinComponents.Workspace.activeClient = selectedItem.client;
-                heap.activated();
+                activated();
             }
             break;
         default:
diff --git a/src/effects/private/qml/WindowHeapDelegate.qml b/src/effects/private/qml/WindowHeapDelegate.qml
index 6d8552bd6a..4f19cc95aa 100644
--- a/src/effects/private/qml/WindowHeapDelegate.qml
+++ b/src/effects/private/qml/WindowHeapDelegate.qml
@@ -4,15 +4,14 @@
     SPDX-License-Identifier: GPL-2.0-or-later
 */
 
-import QtQuick 2.12
-import QtQuick.Window 2.12
-import org.kde.kirigami 2.12 as Kirigami
+import QtQuick 2.15
+import QtQuick.Window 2.15
+import org.kde.kirigami 2.20 as Kirigami
 import org.kde.kwin 3.0 as KWinComponents
 import org.kde.kwin.private.effects 1.0
 import org.kde.plasma.components 3.0 as PC3
 import org.kde.plasma.core 2.0 as PlasmaCore
 
-
 Item {
     id: thumb
 
@@ -20,13 +19,15 @@ Item {
     required property int index
     required property Item windowHeap
 
-    readonly property bool selected: thumb.windowHeap.selectedIndex == index
+    readonly property bool selected: windowHeap.selectedIndex === index
     //TODO: move?
     readonly property bool hidden: {
-        if (thumb.windowHeap.showOnly === "activeClass") {
-            return thumb.windowHeap.activeClass !== String(thumb.client.resourceName); // thumb.client.resourceName is not an actual String as comes from a QByteArray so === would fail
+        if (windowHeap.showOnly === "activeClass") {
+            // client.resourceName is not an actual String as comes from a QByteArray so === would fail
+            return windowHeap.activeClass !== String(client.resourceName);
         } else {
-            return thumb.windowHeap.showOnly.length && thumb.windowHeap.showOnly.indexOf(client.internalId) == -1;
+            return windowHeap.showOnly.length !== 0
+                && windowHeap.showOnly.indexOf(client.internalId) === -1;
         }
     }
 
@@ -38,15 +39,15 @@ Item {
     //scale up and down the whole thumbnail without affecting layouting
     property real targetScale: 1.0
 
+    property DragManager activeDragHandler: dragHandler
+
     // Swipe down gesture by touch, in some effects will close the window
     readonly property alias downGestureProgress: touchDragHandler.downGestureProgress
     signal downGestureTriggered()
 
-
-
     Component.onCompleted: {
-        if (thumb.client.active) {
-            thumb.windowHeap.activeClass = thumb.client.resourceName;
+        if (client.active) {
+            windowHeap.activeClass = client.resourceName;
         }
     }
     Connections {
@@ -62,15 +63,15 @@ Item {
         if (effect.gestureInProgress) {
             return "partial";
         }
-        if (thumb.windowHeap.effectiveOrganized) {
+        if (windowHeap.effectiveOrganized) {
             return hidden ? "active-hidden" : "active";
         }
         return client.minimized ? "initial-minimized" : "initial";
     }
 
     visible: opacity > 0
-    z: thumb.activeDragHandler.active ? 1000
-        : client.stackingOrder + (thumb.client.desktop == KWinComponents.Workspace.currentDesktop ? 100 : 0)
+    z: activeDragHandler.active ? 1000
+        : client.stackingOrder + (client.desktop === KWinComponents.Workspace.currentDesktop ? 100 : 0)
 
     component TweenBehavior : Behavior {
         enabled: thumb.state !== "partial" && thumb.windowHeap.animationEnabled && !thumb.activeDragHandler.active
@@ -160,7 +161,6 @@ Item {
         anchors.bottomMargin: -height / 4
         visible: !thumb.hidden && !activeDragHandler.active
 
-
         PC3.Label {
             id: caption
             visible: thumb.windowTitleVisible
@@ -213,7 +213,7 @@ Item {
                 y: (thumb.client.y - targetScreen.geometry.y - (thumb.windowHeap.absolutePositioning ?  windowHeap.layout.Kirigami.ScenePosition.y : 0)) * (1 - effect.partialActivationFactor) + cell.y * effect.partialActivationFactor
                 width: thumb.client.width * (1 - effect.partialActivationFactor) + cell.width * effect.partialActivationFactor
                 height: thumb.client.height * (1 - effect.partialActivationFactor) + cell.height * effect.partialActivationFactor
-                opacity: thumb.client.minimized || thumb.client.desktop != KWinComponents.Workspace.currentDesktop ? effect.partialActivationFactor : 1
+                opacity: thumb.client.minimized || thumb.client.desktop !== KWinComponents.Workspace.currentDesktop ? effect.partialActivationFactor : 1
             }
             PropertyChanges {
                 target: icon
@@ -278,7 +278,6 @@ Item {
         }
     }
 
-
     PlasmaCore.FrameSvgItem {
         anchors {
             fill: parent
@@ -295,7 +294,7 @@ Item {
 
     HoverHandler {
         id: hoverHandler
-        onHoveredChanged: if (hovered != selected) {
+        onHoveredChanged: if (hovered !== selected) {
             thumb.windowHeap.resetSelected();
         }
     }
@@ -331,11 +330,12 @@ Item {
             }
         }
     }
-    property DragManager activeDragHandler: dragHandler
+
     DragManager {
         id: dragHandler
         acceptedDevices: PointerDevice.Mouse | PointerDevice.TouchPad | PointerDevice.Stylus
     }
+
     DragManager {
         id: touchDragHandler
         acceptedDevices: PointerDevice.TouchScreen
@@ -384,7 +384,7 @@ Item {
 
     Component.onDestruction: {
         if (selected) {
-            thumb.windowHeap.resetSelected();
+            windowHeap.resetSelected();
         }
     }
 }
diff --git a/src/effects/windowview/qml/main.qml b/src/effects/windowview/qml/main.qml
index 72f4e53df9..72de412053 100644
--- a/src/effects/windowview/qml/main.qml
+++ b/src/effects/windowview/qml/main.qml
@@ -4,9 +4,9 @@
     SPDX-License-Identifier: GPL-2.0-or-later
 */
 
-import QtQuick 2.12
-import QtQuick.Layouts 1.4
-import QtGraphicalEffects 1.12
+import QtQuick 2.15
+import QtQuick.Layouts 1.15
+import QtGraphicalEffects 1.15
 import org.kde.kwin 3.0 as KWinComponents
 import org.kde.kwin.private.effects 1.0
 import org.kde.plasma.core 2.0 as PlasmaCore
@@ -26,12 +26,12 @@ Item {
     readonly property int animationDuration: PlasmaCore.Units.longDuration
 
     function start() {
-        container.animationEnabled = true;
-        container.organized = true;
+        animationEnabled = true;
+        organized = true;
     }
 
     function stop() {
-        container.organized = false;
+        organized = false;
     }
 
     Keys.onEscapePressed: effect.deactivate(animationDuration);
@@ -150,9 +150,9 @@ Item {
                 switch (container.effect.mode) {
                     case WindowView.ModeWindowClass:
                     case WindowView.ModeWindowClassCurrentDesktop:
-                        return "activeClass"
+                        return "activeClass";
                     default:
-                        return selectedIds
+                        return selectedIds;
                 }
             }
             layout.mode: effect.layout
@@ -168,9 +168,9 @@ Item {
                     switch (container.effect.mode) {
                         case WindowView.ModeCurrentDesktop:
                         case WindowView.ModeWindowClassCurrentDesktop:
-                            return KWinComponents.Workspace.currentVirtualDesktop
+                            return KWinComponents.Workspace.currentVirtualDesktop;
                         default:
-                            return undefined
+                            return undefined;
                     }
                 }
                 screenName: targetScreen.name
@@ -178,8 +178,8 @@ Item {
                 filter: effect.searchText
                 minimizedWindows: !effect.ignoreMinimized
                 windowType: ~KWinComponents.ClientFilterModel.Dock &
-                        ~KWinComponents.ClientFilterModel.Desktop &
-                        ~KWinComponents.ClientFilterModel.Notification;
+                            ~KWinComponents.ClientFilterModel.Desktop &
+                            ~KWinComponents.ClientFilterModel.Notification
             }
             delegate: WindowHeapDelegate {
                 windowHeap: heap