Also, if you're up for the self-hosted life, what comes next is a music server. If you have good access to WiFi or unlimited data, this eliminates storage as a bottle neck. I recommend Navidrome. But something like Jellyfin or Plex can do Movies and TV, if you want a 1 size fits all.

If you're not, look into Syncthing. You chose a folder on your computer and one on your phone and this app keeps them in sync. After that, my favorite player was GoneMad. It's offline, with real support for music tags. This allowed song ratings and real smart playlists

Make the record labels rich so that they can sue and bully people thank you!