Index: sources/gui/qml/components/ModalDialog.qml
===================================================================
diff -u -r3e682c5afdadcf4dd2006e3d975fbee58e48619e -rc2f474ff07c98aa350c445a2474976a3cf985f40
--- sources/gui/qml/components/ModalDialog.qml	(.../ModalDialog.qml)	(revision 3e682c5afdadcf4dd2006e3d975fbee58e48619e)
+++ sources/gui/qml/components/ModalDialog.qml	(.../ModalDialog.qml)	(revision c2f474ff07c98aa350c445a2474976a3cf985f40)
@@ -16,7 +16,10 @@
 // Qt
 import QtQuick 2.12
 import QtQuick.Controls 2.12 // Dialog
+import QtGraphicalEffects 1.12
+/* Qt6 Port: replace the above import with the following one:
 import QtQuick.Effects
+*/
 
 // Project
 //  Qml imports
@@ -67,12 +70,24 @@
         radius          : Variables.dialogRadius
 
         layer.enabled   : showDropShadow
+        layer.effect: DropShadow {
+             id: _dropShadow
+             horizontalOffset: 4
+             verticalOffset  : 4
+             radius          : 12
+             samples         : 32
+             color           : Colors.dropShadowDialogColor
+             source          : _backgroundRect
+             anchors.fill    : _backgroundRect
+        }
+/* Qt6 Port: replace above DropShadow with following RectangularShadow:
         layer.effect: RectangularShadow {
             id: _dropShadow
             radius          : 12
             color           : Colors.dropShadowDialogColor
             anchors.fill    : _backgroundRect
         }
+*/
 
         // 👇 Placeholder for an injected component. Ex. numpad
         Item { id: _backgroundItem }