There is always something broken on Disney +, especially if you are on the Hotstar version of the app.
It was broken for me as well. But Hotstar Dev Team shared a patched Apk which solved the issue.
Broke since the 7 October update on Sony X90J 😑
I'm not getting Atmos on my A80j as well. Only getting DD 2.0 on Atmos streams. Not even 5.1
Can confirm on 950H, Disney+ internal app is only outputting Stereo PCM. Chromecast passes Atmos.
How do you tell it's broken
Temporary workaround (working for me at least on my A80J and Nvidia shield): cast from a phone or tablet using the Disney Plus app.