QT5 -> QT6: ASSERT: "!d->offscreenWindow->handle()"

[Lukasz4282]

Hey guys, i'm making this post regarding the migration of a certain MS Teams competitor to QT6.
After updating the QtQuick.Controls import from 1.4 to 2.15, I get a runtime library error as follows:

ASSERT: "!d->offscreenWindow->handle()" in file J:\qt_build\workspace\src\qt\qt-6.4.0\qtdeclarative\src\quickwidgets\qquickwidget.cpp, line 1163
Debug Error!

Program: ...spark\build_vscode\output\bin\Debug\dependencies\Qt6Cored.dll
Module: 6.4.0
File: J:\qt_build\workspace\src\qt\qt-6.4.0\qtdeclarative\src\quickwidgets\qquickwidget.cpp
Line: 1163

ASSERT: "!d->offscreenWindow->handle()" in file J:\qt_build\workspace\src\qt\qt-6.4.0\qtdeclarative\src\quickwidgets\qquickwidget.cpp, line 1163

(Press Retry to debug the application)

This is a Windows platform specific issue. Ignoring the error renders the application fully functional, however the error still needs to be fixed. The issue is with QQuickWidget, it has an internal window that shouldn't be mapped to a real window, however, still gets added. I was wondering if anyone else had this occur before and could give pointers.