Check out Navidrome [0]. It's the closest one that I've found. It supports the Subsonic API so there are plenty of mobile apps and probably some desktop ones that work with it. I use play:Sub on iOS.
> I want the ability to rate music across multiple user-configurable dimensions. Add tags. Create smart playlists that interpolate between these.
I'd actually pay for a 3rd party metadata service that doesn't actually provide the music at all, but just let's me tag and rate some across all music streaming services. I've even thought about building that (simply for myself to begin with). I want ratings, instrument tags, mood tags etc. Let me search for songs with 'piano + synth + dreamy + weird' instead of throwing some stupid recommendation my way. And use those tags to find similar tracks across genres and decades of time, instead of just saying "Nirvana and Pearl Jam must be the same because they're early 90s Seattle bands".
I use Airsonic right now, it is basically Jellyfin for a music collection. I use both of these as reliable alternative to Netflix/.../Spotify (where ... is a plethora of other video services such as Disney+).
1. Doesn't use Java
2. Simpler/Quicker to configure
3. More modern webui (though I recently found a good desktop subsonic client, sonixd which somewhat negates this)
Also, I haven't used the airsonic fork, but I was using subsonic before switching to navidrome
I found subsonic to be rather... unreliable. once in a while the database would randomly become corrupted and I'd have to delete the database files and start over. I haven't had any such problems with navidrome, it's been rock solid.