

See Restore items backed up with Time Machine on Mac - Apple Support. With Music closed browse to your Music library folder, ~/Music/Music, then enter Time Machine and restore the database to a recent date before the duplicates were created. Earlier I was suggesting that it was the device that you wiped and reloaded, which you will likely still need to do, but you can either clean up the duplicate playlists manually, or try reverting to an older version of the Music Library.musiclibrary database. Duplicate copies may arise when this syncing process goes wrong. Music has a feature where playlists modified on a device should be able to sync back to the library, updating the original list on the computer.
