Here's the short and sweet.

SoulSeek - an ancient p2p filesharing system that... For some reason, copyright companies don't care about, but until they do, there it is and it's awesome.

Funkwhale - federated dudes all sharing music together, yeah, some of it is copyrighted because of course it is, also an audio server so you get that too.

Jellyfin - Great and modern. Makes a good music server by itself. Only reason it really wins over subsonic and the like is support and upkeep. A lot of subsonic apps are dead.

Plex - Jellyfin (but with corporate overlords)

Find music on SoulSeek, host on Jellyfin, Funkwhale or whatever *sonic fork is still updated, ???, profit is basically the game. Some people also find utility with apps that strip music directly from Tidal and Spotify. Your mileage may vary.