Audio streaming platforms are not exactly the best place to earn money from music. Something like Bandcamp or Steam would be better.
Soundtrack from CI games on Steam
We don’t know what is IA take on it, but the soundtrack author doesn’t mind releasing it on Steam.
CIU could have steam cards but you won’t get any drops for free.
Free apps may only have trading cards if the app has in-app purchases. Users will get a card drop for every $9 USD equivalent spent in the app.
Steam Community Items (Steamworks Documentation)