The trick was to skip the onboarding and go into the Preferences, there was an option there to disable putting your files in the music library folder and messing with the layout

edit: I just compared iTunes 4 and Music in Tahoe and they still have the same preference! It's funny how they clearly did a s/iTunes/Music/, resulting in the "Music/Music" dir https://kalleboo.com/linked/itunes4-vs-musictahoe.png