Hey there ltmaerz,
Thanks for reaching out to the Apple Support Communities.
To get started, we do want to make you aware that this is expected behavior. For more details, check out this link here: Listen to music with Apple Music Voice on iPhone - Apple Support
Tip: If you don’t subscribe to Apple Music, you can get a 7-day free preview of Apple Music Voice by using Siri to play a song or artist in Apple Music. This one-time free preview will not renew. After 7 days, you can subscribe to the Voice plan in the Apple Music app and get a 1-month free trial.
Just to confirm, have you tired canceling the Apple Music Voice subscription and then asking Siri once more to play a song or artist from your Music Library? If not, give that a try and let us know if the issue persists: If you want to cancel a subscription from Apple - Apple Support
As a note, you may need to wait until the end of the Apple Music Voice subscription to give this a try.
Keep us updated on the results, and we'll continue from there.
Have a great day!