How to get VTK9 + Qt6 working together?

@NameRakes Thanks for testing.

Yes, it is still a work-in-progress (WIP). I haven’t yet added all the changes for RenderingQt, QtSQL and ViewsQt modules. However, GUISupportQt and by extension, QVTKOpenGLNativeWidget should be working fine. Were you able to test that? I’d love to see your results. You’d have to disable the other modules for testing, though.