If a toplevel window has its position moved, the entire contents of the window are now repainted. This causes excessive flicker especially in the case of an embedded native window.
This was caused by a fix for
QTBUG-97774 , which ironically was reporting flickering, although that was during resize. It seems like the fix for that bug needs to be constrained specifically to resizing, and not just window position changes.
The offending commit is: [https://code.qt.io/cgit/qt/qtbase.git/commit/?id=000f1ee3604048f693f2a9425948a37ec45b4301|000f1ee360]
Attached is a simple reproducer application: QtWidgetFlickerTest.7z
And a small video showing the issue: Qt5_vs_Qt6_EmbeddedWindowFlickering.mp4