The screenshots show it’s not just a rating, you can add text to them. Am I misunderstanding you?

Have you tried Piper?

I was using Plexamp for a while but now I’ve mostly converted my library to OPUS so I can fit it all on my phone. I have a script to automatically copy the directory structure/artwork and convert from my main FLAC library, and keep it in sync with my phone using syncthing. I use Musicolet for playback. If your library is bigger or you don’t have much free space then this is of course not an option, but it works for me.