Apple's new Music app absolutely ruined my entire local music collection one day, when updating from macOS 11.4 to 11.5 (I think).

My music collection traveled with me from OS update to OS update for about 13 years with no problem. And now pretty much everything is broken, some files can not be played even though they are on disk, half of the album covers are gone, syncing with the phone gives a ton of errors. What happened to this app and why - I have no idea. It was my worst day as a long-time Apple user and needless to say how maddening it was. Oh, the backups don't help, the new app does the same thing to the backup copy too.

Seems like Apple doesn't care about your local music collection anymore, nobody even bothered to test.