Funkwhale is the best option for replacing Spotify. It can be private or public and federated so you can follow users who want to share their playlists and such.

Navidrome is another good option although i don’t use it personally I hear nothing but good things.

Avoid subsonic directly but youll find funkwhale and other services support it as a protocol very well. Its just the subsonic server software itself and all of the forks seem to basically just be reinventing the same wheel over and over so they can charge for “premium” features.