Music app on Catalina gets stuck
Try this, which worked for my colleague while he also had a similar kind of issue after upgrading macOS to Catalina:


Move your music out of the Music folder and delete everything left in it.
go to ~/Library and remove any folders that have Music or iTunes in the name
go to ~/Library/Caches and delete any folders with Music or iTunes in the name
Reboot
Put your music folders back where you had them before. You may need to Import your music again to let the Music app organize them in a way that makes sense to it


After doing this, it should fix your issue.