I thought the thing will lower your phone into the box so that the battery doesn’t take your whole room with it when it eventually explodes during charging…

Yeah, Synology and NFSv4 is a bit hit or miss if you don’t use a Kerberos server. I’ve experimented with that back in 2018 to no avail: https://blog.mbirth.uk/2018/01/05/synology-nfsv4-with-id-mapping.html

Well, it’s not a protocol, Subsonic is an app that became pretty famous in the MP3 era and had a nice API for which various clients were developed.

The source code was Open Source in the early days which was forked into e.g. AirSonic, MadSonic, LibreSonic.

Those projects are dormant for a few years now. That’s why new ones have emerged that simulate the same API so all the client apps can still be used with them.

EDIT: Looks like these are projects that support the Subsonic API and are still in active development:

• Funkwhale (also: federated)
• Navidrome
• Gonic
• Airsonic-Advanced
• LMS
• Astiga
• Nextcloud/ownCloud Music
• SupySonic (headless server)