You can self-host something like Navidrome/Ampache and use a subsonic app like Amperfy https://github.com/BLeeEZ/amperfy https://github.com/BLeeEZ/amperfy and d

You can self-host something like Navidrome/Ampache and use a subsonic app like Amperfy https://github.com/BLeeEZ/amperfy https://github.com/BLeeEZ/amperfy and download your whole library (or cache as you go along playing tracks).