So I've been facing this problem for a while and it's super annoying at this moment, always that I go from one app to another, let's say from Youtube to Disney+ in the Apple TV, the sound on the tv goes from 50 to 0 and some seconds later from 0 to 50 again but the Beam stops reproducing sound, like if it was muted.
And then I have to restart the Apple TV to start listening any sound again, this happens always that I go from one app to another so it's not related to the apps. Sometimes going back to the Apple TV Home restores the sound but sometimes doesn't.
I'm using a Ugreen HDMI 2.1 8k cable on the eArc spot of my TV.