Not OP, but when I was looking for an alternative it was the music analysis and Auto-Playlist/DJ features that set Plexamp apart.

Nothing wrong with having to pay for software if the prices are reasonable. It’s a product like any other, with real people working on it.

I’m using the Beeper Matrix server, but self-host their bridges. That way the de- and reencryption is done on my server, and Beeper only sees encrypted Matrix messages. It’s extremely easy to set up if you’ve used docker before, much less work than running a full Matrix server yourself.