Atmos is working flawlessly on my Gen 1 ATV4k. I noticed that 2 of my Denon's 7 rear HDMI inputs are free. I think I will connect my Gen 2 unit for testing purposes as new tvOS versions come out.Thank you for the report. I won't be updating my OS! I'm still on the OS that's several stages old and it works ok for Atmos. I will continue to do that until I hear good things on here about the new updates. Such a shame they can't get this right. They NEED to just drop Atmos altogether if they can't support it. As far as I'm concerned, it is false advertising to claim the Apple tv4k 2nd gen supports Atmos. The public has no idea when they buy one, and then find out later.
Apple has released beta 3 of tvOS 15.3 to developers, and it has not fixed the Atmos problem according to that other thread I posted a link to several days ago. Here it is again:
Netflix Dolby Atmos problems with new Apple TV 4k