Reproducible case: The "notepad" example from both qt5 and qt6. Attached videos only use the qt6 version but qt5 is also affected.
Description: If a QToolBar is set to be floatable, it could be managed as an independent window and have it's own position. It can also be "docked" back into the main window if it is dragged to the appropriate position.
However, this behavior is broken under wayland. The floating QToolBar always stay in the middle of the main window and there is no spot for docking back the QToolBar (or I couldn't find it). The attached videos could explain this behavior better.
xorg.mp4 is the expected behavior under xorg display server while wayland.mp4 is the broken behavior under wayland display protocol.