I’m having the same issue with ATV+ content. I’m getting 2.0 channel audio when the shows clearly say 5.1 on the description (as you pointed out)
Since when did Apple TV become available on Chromecasts/Android TV?
Not just you but there are some titles that trigger Atmos!
Dolby Atmos still not working on Apple TV+ using Chromecast with Google TV... very disappointing.
It depends on the movie and possibly what country. So far I've found Black Panther, Guardians of the Galaxy 2, Lord of the Rings Return of the King Extended, Men in Black. No Idea how or why certain titles have Atmos.