This is an edgy case defined by ToS, that's why it won't be supported by Jetispot (and that's why it is not available in librespot)

In fact that's possible, but I don't want to get into legal trouble.

Very much that last part 👏👏👏👏

I'm not sure if this would work and how hard it would be to implement, but could it be possible that the app generates an encryption key once opened for the first time (that the user cannot access) and to then download music and saves it encrypted so it can only be listened to from within the app? I respect your choice if you don't want to include a download function, I just wanted to share my idea.

What about the implementation of something like SpotiFlyer in-app that uses YouTube or Jio Savn to query and download songs, saves to storage, and is playable within the app?