Apple Music Library duplicates

Hold Option and choose File > Library > Show Exact Duplicate Items, then sort by Date Added so the copies the sync made sit together, select them and Delete from Library (pick Keep File if it asks, both entries usually play the same file). With Sync Library on, that delete reaches your other devices too. Katalog (musickatalog.com) runs alongside the Music app, and its File > Find Songs Listed Twice in Music counts the extras and saves a list before you delete anything.