Not sure if Artesian has already experimented with this or not, but it sounds intriguing:
".. It doesn't take calls, send messages, and there's no SIM card in it. All that phone does is sit on a shelf and host my music library, using a tool that's likely the perfect self-hosted music server.
It happens to be the best music server I've used, and it cost me nothing except some time during setup. Most of us have old phones like that. Too good to recycle, not good enough to use daily, but still perfectly functional. So, if you are looking for a new way to use that old phone, or want a music server that doesn't put a hole in your wallet, hosting a music server on your old Android can be the answer.
Why your old phone beats a real music server
It’s already paid for, always on, and surprisingly capable ... A desktop or laptop would honestly be wasted holding only a music server. .. The only challenge is to convince Android to let a long-running process live in the background, and to do some basic setup.
How I turned stock Android into a music server
No root, no hacks—just a few smart tools
The easy part is that you do not have to unlock the bootloader or flash another OS. Termux and Navidrom are all the tools you need. You could flash your phone to something like PostmarketOS or LineageOS for better control, but you don't need to in case you still want Android on the phone....
Navidrome is a lightweight, self-hosted music streaming server that lets you stream your personal music library from any device.
Living with a phone-powered music server is shockingly good
Tiny, silent, cheap—and it just works
Once the service is up and running, you never need to touch the phone again.
Full article:
https://www.makeuseof.com/old-android-host-better-music-server-than-expect/