sadly tomahawk is mostly maintenance mode, or it is dead? https://github.com/tomahawk-player/tomahawk "There is noone working on it. There isn't much sense in adding any new issues in the issue tracker unless you want to fix them yourself." I can't tell because there are still commits everyone in a while ¯_(ツ)_/¯
Do you have a premium Spotify account? If so, you can try Tomahawk. Last time I checked you can sign in to a bunch of different services.
https://github.com/tomahawk-player/tomahawk-android/blob/master/README.md
Since you want something local there is no need to "self host" anything..
I knew this one but it's abandoned. Not sure if an alternative exists..
https://github.com/tomahawk-player/tomahawk
If you really want to self host you'll be able to do this with Navidrome but you wont listen from instagram or anything else that's not your hosted library
It's essentially abandoned but I would give Tomahawk a shot. Their goal was to integrate as many music services as they could. You can even listen along with other people in it.
You can try Tomahawk Player, but it had pretty basic Spotify functionality back in the day. I think you weren't able to play your Spotify playlist without importing them to Tomahawk.
It's entirely possible; it's just unlikely.
Tomahawk supports a lot of services natively. With the help of the open source community helping them you can grab a Google Music plugin.
It all works wonderfully and will only get better if(when?) Google releases a Music API.