When undocking a dock widget, it turns into a normal desktop window (xdg-shell) whose movement is handled by the compositor and the application is not aware of its position. Qt seems to expect a windowing system with global coordinates where it could detect the movement positions; no support has been developed for redocking on Wayland it seems

Also, while moving the dock widget by its header without releasing the mouse button, changing the side of the window is actually possible, but there's no visual feedback — the dock widget stays in the center of the screen.

I'm not sure what would be the best way to do QDockWidget on Wayland, but maybe have these widgets as subsurfaces with custom movement functionality inside the window, never turning them into standalone xdg-shell windows?