Outertune, Harmony, etc. kept dying on me too, so I pulled the nuclear option and set up a Jellyfin server for my music. yt-dlp can download whole playlists, so I had it pull the 250-ish songs I regularly listen to from youtube. I use FinAmp as the music app on my phone now, it's set to automatically download the songs I add to my Jellyfin.
Only thing I haven't figured out yet is how to find out about new music, but at least I'm now always guaranteed to have something that works.