Dumb q but did you ever have apple tv -> tv -> sonos soundbar set up in a way where you were able to control the sonos soundbar audio from the iphone remote app?

I have a samsung home theatre audio system and all the basic functions such as volume control, mute, and power control is possible from an actual apple remote or the same apple remote app on an iphone.

Yes, LC OLED to Sonos Arc. Works a treat. At one point the remote started malfunctioning and I had to cover the IR transmitter with tape, but otherwise extremely reliable. Remote on iPhone works fine to control volume. The only thing is that if you add other Sonos speakers (say, in the kitchen as well as TV room) the mute only mutes the TV.