TCL 55S535 not recognizing ATMOS/5.1 soundbar - Vizio M512a-h6. Says only Stereo is available.

I know this is an old topic, but I had a similar issue where I would lose access to control the sound with the remote. Dolby Atmos wouldn't be listed under Digital Output Format, not would the sound bar be listed under the CEC settings.

Step 2 on this link solved it for me, hope this helps:

https://www.trustedreviews.com/how-to/hdmi-arc-and-cec-not-working-try-these-fixes-4041394#:~:text=Where%20HDMI%2DCEC%20isn't,and%20then%20power%20them%20on.