I started out with one system - an Arc. Whenever I watched TV, the Sonos app would show something like TV audio - Dolby 5.1. Along with that, there was an option to increase/decrease the volume or even mute it. At one point, I decided to briefly play iHeartRadio on the arc. That now ALWAYS shows up.
I recently added to my system (second TV) an arc, sub, and Era 100’s. I briefly saw the audio control options in the app when I selected the room and then viewed that system. Now the audio controls are missing for the new system and iHeartRadio still shows up.