Ok. I have contacted my legal team (I work in the Legal field). And I asked if we can start a class action suit against TMobile for the dreaded challenge of these apps not working on mobile data being there is perk that if you sign up for a specific plan, you are entitled to music and not use your monthly data. Heck it's why I change from the 30 to 40$ plan...
I have since opened 3 tickets. No resolution.
I will say the work around is to use (Proton VPN APP is free) a VPN. Once you enable it, bam the music works on mobile data. You can disconnect the VPN and the music app still works.
Now I also understand the APN hack to change to IP4 which does work but not 100%. But then your traveling at IP4 on all your apps...
So the real challenge actually isn't TMobile but the actual music vendor not supporting IP6.
So a class action suit would raise corporate eyebrows but in the end it's the fact of Spotify not on the IP6 level.