More or less similar to QTBUG-136739, but the situation is much more on Windows. The same reproducer can be used. Still, build it against 6.8.3 or 6.9.0 to see the problem. There is no choice for QPA on Windows so just leave it. And regardless of graphics backend (as opposite to what is described in QTBUG-136739 that at least Vulkan and Software should work on Linux), glitches happen on Windows.

I've also uploaded a screen record. You can see that the layout of window and window itself "flashes" like crazy. One big difference I can see is that the "wobbling" is not a problem here. The window position is pretty much fixed. But resizing and render glitches on bottom/right edge is serious.