One of the annoyances I’ve found in switching from Mojave to Big Sur (skipping Catalina) is that smart playlists are broken in Music.app:
- Create a smart playlist (containing songs from several albums)
- Switch to Songs view in natural sorted order
- Reorder some of the songs
- Quit Music.app and restart it
- Expected behaviour: the playlist retains its natural order
- Actual behaviour: the playlist has been resorted in order of Artists and Albums
It’s been like this in every version of Music.app that Apple have released since I upgraded to Big Sur. I reported it in Apple’s “Feedback Assistant” (their successor to Bug Reporter / Radar) a while back.