Not what youre looking after but- I use newpipe as a peertube client, but since it supports youtube as well you can search yt music specifically and download a track in up to a 128kps .m4a of 160kps .opus file. I then use vlc for android to play em, and it works just fine :3 You may find a offline music player with a ui similar to vi as well!

Some minor gripes is that these files seemingly dont come with metadata, and you cant download a whole playlist or album at a time, both being huge bummers :/