iOS / iPad os does support ATMOS for movies and TV with AirPod pro and max.
It's also supported on the aTV on headphones, not just homepods.
To check, while watching something, go to the audio settings, (control center -> long press volume slider) where the ANC settings are, Just under the volume slider, it will show you the type of audio it's playing.
Just tried it with my APP2 and a TV show on aTV+ (for all mankind).
I tried it with only one APP in, and got "atmos available", put the second one in, and it switched to "atmos"