Are you using the TV’s native apps? Do you have a Netflix Premium subscription and the “ad-free” Prime Video subscription?

I am using the TV's native apps, I don't have premium Netflix but I do have the ad-free prime. 

Dolby Atmos is only available on Netflix with a Premium subscription. 

Try testing the film The Tomorrow War on Prime Video.

Also be sure to set the Digital Audio Out setting on the TV to Pass Through.

I just tried The Tomorrow War and the Sonos app is saying it was playing Dolby Digital Plus plus 5.1

I checked and it is on pass through as well. 

Also just tried a movie on my ps5 with Disney+ and it shows it playing Dolby Atmos. 

Are you 100% sure you have the “ad-free” Prime subscription? If so, Dolby Atmos may not be supported on the TV’s native Prime Video app.

Now that you mention it I don't pay for the upgraded ad-free version. 

Paramount+ I have a premium account and it plays in Dolby Digital 5.1 when the movie descriptions says it has Dolby Atmos. 

Do you have the Paramount+ with Showtime plan? Does your TCL TV use an Android or Roku OS?

I have that plan. It's the Google version. 

According to Paramount+, it should work:

If you have the Paramount+ with SHOWTIME plan, you can stream movies with Dolby Atmos, which is a popular surround sound format! Currently, Dolby Atmos streaming is available on these devices:

• iPhone or iPad
• Apple TV
• Android TV (version 9+ supported by Dolby Atmos technology)
• Fire TV
• Google TV
• Roku TV

Hi ​@LJ1000 

Welcome to the Sonos Community!

Sorry to hear of this issue you are having with playing Atmos content on your new Arc Ultra. 

As you are able to play Atmos, everything to do with your TV and your Arc Ultra is set up correctly - when you don’t get Atmos, that is now presumably due to the TV app used (and possibly it’s settings), the content, or your subscription level.

I hope this helps concentrate your efforts to the right location.