I checked out a few items on HBO Max using an Nvidia Shield.
OAR appears to be intact, nothing I've come across is has been cropped or blown out.
I watched the latest X-Men film, and this was in Dolby Digital Plus.
Dolby Digital Plus works for new programming, but not all. I watched Ben Hur yesterday evening, and the audio was 2.0. The TCM Section is pretty nice if you're into classic movies. I also checked out a few minutes of "How the West was Won" it had a very nice image without the obvious three lens morph that I'm accustom to looking at. You can see the lines, but you have to know what you're looking for. If you're not familiar with the film, then you may not even know that they are present throughout the film.
The Studio Ghibli section was a suprise. I watched a little of Castle in the Sky, and this film had Dolby Digital Plus for audio.
I'm really not expecting HDR or Atmos anytime soon, and I'd rather have them done properly, rather than a quick batch job considering the amount of content that is available for this service.
Marantz SR7010/Marantz MM7025
Oppo UDP-203 - Nvidia Shield
XBox One X
Klipsch RP-260f - RP-440C - RP140sa- RP-160m - RB10 - Sony SA-WM500