It's up to Netflix. Nothing Roku can do about it. Yes, Netflix is really taking their time with their rollout. One more reason I cancelled my Netflix account.
Want to agree with the comment by CSmyre64 about Atmos support. I watched Hobbs and Shaw on Vudu in 4k with full dolby Atmos sound over my Roku Ultra and Denon AVR X6300H on 10/20/2019. On Netflix 4k streaming using the Roku Ultra 4670RW I get a selection for Dolby Atmos/ surround sound in a pop-up box on my TV screen but then the AVR displays Dolby Digital+ +DDS when the pop-up disappears. The Roku literature (and my Denon) states that Atmos is available as a pass through on their units and it sounds great. I've had the same results on HBO and Showtime.
Yes its on Netflix. Netflix requires the device decode the audio not simply pass it through to the receiver for it to decode atmos (or so I have read). Roku passes the audio through so with Vudu and Amazon Prime Atmos works fine.
To me this is a real pain in the neck. Now when i want to watch a netflix atmos show I watch with my apple tv which has a setting set for it to decode all audio. But that setting is a pain to get to so I then use my Roku to watch all shows not in Atmos. I want my Marantz receiver to decode regular Dolby 5.1 because it has a feature to use all 13 of my speakers with an impressive algorithm of dividing up those 5 channels to sound better than regular 5.1. That feature doesn't work on the apple tv since with its setting set to decode audio it does not send dolby 5.1 to my reciever it decodes the dolby 5.1 and sends 5 PCM audio channels to my receiver.
I have no idea why my Marantz receiver can't use its "simulate atmos" algorithm on 5 PCM channels but it can't. Or maybe apple tv could allow more settings in its configuration so I could select it to only decode atmos but it doesn't. But even though there are plenty of ways to fix this problem my ire is directed at Netflix since I know of no sensible reason why they want a less capable video player to decode audio and not receivers dedicated to audio.
With a Roku device that can't decode atmos only pass it through, netflix atmos will never work unless Netflix changes their policy.