Nope using 17.1 on my Apple TV and getting dd 5.1 with no problem 

I can get it briefly to appear by cycling between auto and pass-through but it seems to have a second delay in the audio. If I then close and re-open an app (e.g.) Netflix, it goes back to Stereo PCM

Sounds like a tv issue not Apple or Sonos 

Same thing happing to me . Was not like this before iOS 17 . It’s an Apple issue . 

I ran into sound issue after I moved a 4K Apple TV to a new room, connecting it to my Samsung 4K television and my Sonos play base. I tried making adjustments using the TV button on the Apple TV remote and connecting sound through the updated sound and quick settings button. I also try to go into the sound system settings inside of the Apple TV. I tried going into the settings inside of the Samsung television, as well as Sonos settings. I found the solution in the Apple TV settings, under remotes and devices.  In the home theater control setting, select that the control TVs and receivers is on. Ake sure the volume control is set to auto not HDMI not TV via IR or Samsung via IR. Set to auto to allow   adjusting sound using your remote control and coming out of the Sonos.

I am seeing the same issue with Apple TV 4k only putting out PCM Stereo. I recently purchased a SONOS Arc and noticed in the SONOS app that the audio format is always PCM stereo. My current setup is an Apple TV 4k (latest generation) with an LG EG9100 OLED and a SONOS ARC + Sub.

I thought it might be due to my dated TV and that it does not have eARC (only ARC). To test this, I temporarily swapped out my TV with a newer LG LED TV that has eARC and am seeing the same issue. When I remove the Apple TV 4K from the equation and use an App on the LG TV itself (e.g. Disney +), I see Dolby Digital + and Atmos coming through the SONOS Arc as expected.

I have messed around with all of the Apple TV Audio Output settings to no avail. I am currently going to try upgrading to the latest beta version of TV OS 17 to see if that fixes anything. Also am going to try resetting my Apple TV if the update does not work.

@jordache16 Set the Audio Format settings on the Apple TV to this:

Change Format: On

New Format: Dolby Digital 5.1

It is without a doubt OS related as I have not previously had problems (OS 17.3 beta).. When the sound format is set to auto/standard on my ATV I also experience PCM 2.0.
However, it switches over to Dolby 5.1 if I stream a movie..

If I force ATV to run Dolby 5.1 then I have Dolby all the time..

Since I have a Playbar, it doesn't matter to me that Atmos is switched off, the question is whether there are other settings when you have an Arc connected and can activate/force ATV to play Dolby Atmos.

I tried this and am still getting Stereo PCM. I have updated to OS 17.3 Beta and this did not fix anything.

I am likely going to be returning the SONOS at this point.

Make sure the Digital Sound Out setting on the TV is set to Auto. If this doesn’t work, it’s likely your TV is too old. You might try connecting the Arc to the TV’s optical port instead.

I’m having the same issue of only seeing stereo pcm from Apple TV.  Seems like tvOS 17 was the culprit as I don’t recall the issue before.  I’ve checked everything (cables, changed audio format to 5.1). I am getting 5.1 when signal direct from TV. So frustrating!

After the update yesterday, the challenge is solved with dolby 5.1... At least for me..

New software update 24/1-24

I’m not seeing it fixed on my version. Additionally when I check my TV digital output settings, Dolby digital is greyed out which is what leads me to believe it’s Apple TV related. 

My Apple TV 4K (2 gen) is updated to 17.3 (21K646)
My Samsung S90C is on 1310.3.
SONOS is on 15.11 but was updated on 24/1 with a newer build version, still 15.11

On my Apple TV I have:
Sound out: TV speakers
Audio format: Change format (off) Dolby Atmos (on)
Reduce loud sounds: off

On my TV:
Audio Output: Optical
Digital output format: Auto

For me it works now, also the SONOS App became much faster, no lag when I adjust the volume.