I have an Anthem AVM60, and I get 4K/HDR from Netflix, but I haven't seen Atmos on any of the shows that are listed as having it. My ub820 firmware is up to date. I don't know why that would be.It is possible, but works with some AVR's and electronics, and not with others.
The UB-820 is not *officially* listed as supporting Atmos as a device, by Netflix, and yet many of us do in fact get it. I have a Marantz SR7010, and it gives me 4k/HDR and Atmos when available. A friend had a somewhat older Yamaha AVR and didn't get Atmos, but when he upgraded to a newer model, he did.