Comment by dweymouth

OpenSubsonic (https://opensubsonic.netlify.app) is the closest. It's a collaborative effort to extend and modernize the Subsonic API, which had become a sort of de-facto standard API. Navidrome, Gonic, LMS (Lightweight Music Server, not Lyrion/Logitech), and other servers implement the API, and Supersonic, Symfonium, and other clients consume it. (And it's backward compatible with the original Subsonic, so older Subsonic clients will work, just not support all the new features that have been added.