Mac storage basics · Photos, music and video
Where does the Music app store my songs, and can I change it?
Short answer: Song files live in the Music Media folder set in Music → Settings → Files. Change that location, then use File → Library → Organise Library → Consolidate files to copy them over.
Music keeps its library database in Music inside your home folder, and your song files in the Music Media folder (set in Music → Settings → Files). Apple Music streams and downloads are managed separately by the app.
To put your own song files on another drive, change the Music Media folder location in that settings pane, then use File → Library → Organise Library… and choose Consolidate files so existing songs are copied there. Check the songs play before deleting the old copies, and keep the drive connected when you use Music.