The Apple update might have changed the sound settings on the Apple TV. What are those settings now?

Still on Auto, as it was before. Even turning off Atmos results in Stereo PCM output. 

Hi @Brooktop 

Welcome to the Sonos Community!

If the only change that has been made is that you updated to iOS 18, then I recommend that you contact Apple for assistance - if you are able to play Atmos, then it is very likely that all the settings are as they should be. A reboot of all three devices (unplug TV and Beam from power, restart Apple TV) may help, but I rather doubt it.

I hope this helps.

I having the same issue. I wouldn’t change anything if I were you and just wait for the TVOS update...

Update: YouTube app (the only one seemingly being played in 5.1 according to the Sonos app) is now outputting Stereo PCM with a drop in volume. Strange….

Update: YouTube back to 5.1. DD 5.1 test video working properly. All other apps still Stereo PCM. Even stranger…

Something has happened after the 18.0 update..
In the past I only got 5.1 if I forced the Apple Tv 4K to output 5.1 sound.
After the update I have set Apple Tv 4k to auto and Atmos on auto, now I get 5.1 when it is supported.

I’m happy to report that the recent TVOS 18.1 update has fixed the problem…

I’ve not had an update (even Beta) for weeks. Still getting Stero PCM.

I gave up and got a 4K Fire TV stick.