Despite all of this, I haven’t completely abandoned Plex.
Plexamp remains one of the best self-hosted music applications I’ve ever used.
Lyrion, Music Assistant, and Navidrome are all solid options. And Jellyfin also supports music hosting, along with FinAmp, which has similar functionality to PlexAmp (maybe not as good, but download functionality works).
Personally, I abandoned PlexAmp. Wasn't worth keeping with the rest and it has been downhill since the loss of Tidal integration. Navidrome clients work great, have solid radio and discovery features for large collections, and support local downloading for on the go.
And for local listening, I'd argue that Lyrion with Blissmix or LastFM "Don't Stop the Music" plugins are as good and sometimes better than PlexAmp. And Navidrome and/or Music Assistant with AudioMuse-AI plugin utterly destroys PlexAmp's radio/DJ functionality. Install AudioMuse, scan your library and go, it just works. Especially with recent builds having native Linux, Mac, and Windows now (I deployed with Docker compose before these options were available).