When I go on vacation I prefer to keep my smartphone with WiFi and mobile data off, but I really don’t like the way Spotify handle offline content. Most of the time it doesn’t download everything and when I do a research, it show me even content that’s not available offline (how can it do that?). Is there a selfhosted service that I can use to download my playlists and play them with an Android app that can download them?
I don’t know that the specific thing you want is available (Spotify but it has better downloading).
However, the tool I linked (zotify) does let you download playlists from Spotify (as files). Then you can put the files into a self hosted tool for the actual listening. If you’re mainly using Spotify and trying to get songs to be synced to another service for offline use then that seems like a lot of work.
If you’re willing to pay, you could just try a different service (Tidal, Qobuz, or Apple/Google offerings) and see if you like them better.