Super Slow Musescore Startup - Potential Fix
If you are having really slow boot up on MuseScore on Windows 10, try setting your default printer to "Microsoft print to PDF." It went from occasionally crashing and 30-60 second boot times to 1 or 2 second boot times for me.
If you are able to open MuseScore:
File - print - right click "Microsoft print to PDF" - Set as default printer
If you are having trouble it's worth a shot.