As far as I get it, subsonic has an open API implemented by navidrome and a few other open source servers. All subsonic compatible apps will work.
For Android the best is by far Symphonium, but it a paid app (well worth it).
Otherwise tempus is another valid and open source app.
And no, subsonic (and navidrome) has nothing to do with audiobooks or podcasts. I selfhost both navidrome and audiobook shelf to cover all cases, and I am pretty comfortable.
