Run-time issues with Qt 6-based build of Qt Quick Designer

When building Qt Creator (master branch) with Qt 6 and launching it with the Qt Quick Designer plugin enabled, this warning appears:

Qt::AA_UseOpenGLES is no longer supported in Qt 6

...also...

SOFT ASSERT: "hasFpsHandler" in file C:\Users\alportal\dev\tqtc-qtc-super\qtcreator\src\plugins\qmldesigner\qmlpreviewplugin\qmlpreviewplugin.cpp, line 89

qtc.qmldesigner.theme: Couldn't load "C:/Users/alportal/dev/tqtc-qtc-super/build-qtcreator-Qt_6_1_0_win32_msvc_e683f2-Debug/share/qtcreator/qmldesigner/propertyEditorQmlSources/imports/StudioTheme/InternalConstants.qml" due to the following error(s):
qtc.qmldesigner.theme: "file:///C:/Users/alportal/dev/tqtc-qtc-super/build-qtcreator-Qt_6_1_0_win32_msvc_e683f2-Debug/share/qtcreator/qmldesigner/propertyEditorQmlSources/imports/StudioTheme/InternalConstants.qml:32:15: Invalid property assignment: \"name\" is a read-only property"

When opening a .qml file in design mode, Qt Quick Designer would display a dialog (see QTCREATORBUG-25630) and crash.

If I set the fix Qt Quick backend to OpenGL (see: https://codereview.qt-project.org/c/qt-creator/qt-creator/+/345338 ), and fix the "name" is a read-only property issue above, Qt Quick Designer will show up, but with a blank Property editor:

Could not load image: "C:/Users/alportal/dev/tqtc-qtc-super/build-qtcreator-Qt_6_1_0_win32_msvc_e683f2-Debug/share/qtcreator/qmldesigner/propertyEditorQmlSources/imports/HelperWidgets/imagesdown-arrow.png"
From Qt 6.2, QFont::setFamily() will no long split the family string on the comma and will keep it as a single family
qt.qml.compiler: file:///C:/Users/alportal/dev/tqtc-qtc-super/build-qtcreator-Qt_6_1_0_win32_msvc_e683f2-Debug/share/qtcreator/qmldesigner/propertyEditorQmlSources/imports/HelperWidgets/ItemFilterComboBox.qml:59:52 Parameter "index" is not declared. Injection of parameters into signal handlers is deprecated. Use JavaScript functions with formal parameters instead.
file:///C:/Users/alportal/dev/tqtc-qtc-super/build-qtcreator-Qt_6_1_0_win32_msvc_e683f2-Debug/share/qtcreator/qmldesigner/propertyEditorQmlSources/QtQuick/ItemPane.qml:449:21: Type LayerSection unavailable
file:///C:/Users/alportal/dev/tqtc-qtc-super/build-qtcreator-Qt_6_1_0_win32_msvc_e683f2-Debug/share/qtcreator/qmldesigner/propertyEditorQmlSources/QtQuick/LayerSection.qml:46:28: RegExpValidator is not a type
file:///C:/Users/alportal/dev/tqtc-qtc-super/build-qtcreator-Qt_6_1_0_win32_msvc_e683f2-Debug/share/qtcreator/qmldesigner/propertyEditorQmlSources/QtQuick/ItemPane.qml:449:21: Type LayerSection unavailable
file:///C:/Users/alportal/dev/tqtc-qtc-super/build-qtcreator-Qt_6_1_0_win32_msvc_e683f2-Debug/share/qtcreator/qmldesigner/propertyEditorQmlSources/QtQuick/LayerSection.qml:46:28: RegExpValidator is not a type
void __cdecl QmlDesigner::readSharedMemory(int,class QmlDesigner::ImageContainer &) Not able to create image: 0 0 0
void __cdecl QmlDesigner::readSharedMemory(int,class QmlDesigner::ImageContainer &) Not able to create image: 0 0 0