MuseScore 4 locks upon opening in Windows 11

When opening MuseScore 4, the Scores window locks up with no response to any key press or mouse click, except fault tone. Occurs on every attempt to open MuseScore 4, with no difference in opening directly or through Muse Hub. The only way to close the application is to use Task Manager.
I have uninstalled and reinstalled MS4 several times -- the same fault occurs.
Interestingly, opening a second instance of MuseScore 4 (by rightclicking MS4 icon in task bar), that instance works normally, but sometimes very slowly.
First two weeks or so after initial installation, MuseScore 4 worked, but had some crashing issues. The Lockup may have started after I attempted (unsuccessfully) to download various sounds via Muse Hub.