I am convinced it is not the Sonos update nor the hardware that is the issue.
I am convinced that is a combination of the other two components of my system: the Hisense TV and Disney+.
Disney and Hisense have updated their stuff to support the IMAX formats and DTS:X presentations from within Disney. Only a few manufacturers have been deemed worthy for the IMAX upgrade and Hisense was one of them. While that does not affect Sonos directly, I feel that in their haste to update these things, some things were inadvertently changed. I have no other proof other than the lost Atmos on Disney + while Atmos still functions perfectly on my other apps (Netflix and Amazon).
My solution for my own use was this: I moved an Apple TV 4K from another tv in the home and connected it to the Hisense tv. The result was the immediate return of Atmos to Disney + and a huge improvement of picture quality when compared to the internal apps of the Hisense. Frankly, I was hugely surprised at the improvement of picture quality.
Recognizing that this is a Sonos forum, I do not want to praise Apple too much, but I was very pleased to have Atmos returned to my Sonos system.
I am sure that at some point Disney and Hisense will figure this out, but I will keep the Apple TV connected and bypass their internal apps.
Good luck to everyone looking to solve similar problems!