Cannot drag Preferences or Style windows with mouse (Ubuntu)
OS: Ubuntu 20.04.2 LTS, Arch.: x86_64, MuseScore version (64-bit): 18.104.22.1688021370, revision: 3224f34
Normally, if you click on the title bar of a window you can drag it. However, in Ubuntu, the Preferences and Style windows cannot be dragged at all. Other windows, such as the Synthesizer and Mixer can be dragged OK.
If you reduce the size of the MuseScore window so that it smaller than the screen, then try to move a Preferences or Style window, both window and sub-window move together. Perhaps this is a clue to the underlying issue.