I'm cleaning out my gmail folders this weekend, and went deep into the archive to 2011, when I got my invite to Google Music.
It's funny, because I just (November) moved all of my music out of cloud and back to local-only. Amazon was the last straw, when I tried to play purchased music, and was forced to listen to it on shuffle with other songs not of my choosing.
Anyway... there was a time when Google (ahem, Youtube) Music was set to be a game-changer. Imagine if enshittification wasn't a thing.
I have had Emby forever. Love it for videos, but it's absolutely garbage for music. It's just not built to support music, so it's clunky and slow. I never used plex or jelly, but both built stand-alone music apps to address this exact problem, so I would assume they are both better. Emby was asked to build one, but they basically said no and also not anytime soon if they ever do decide to. They really didn't seem to get what was so bad with what they already offered.
There are standalone music apps for emby though, I use symfonium on android which is simply awesome. It's not that expensive either.
There is no official standalone music app for jellyfin. The regular apps do great with music though