Finally got around watching some HDR content from Disney + and other paid download services.
[SPOILERS!!!!]
With Avengers Endgame and viewing at arm's length. The beginning portion with Iron Man stranded in the ship, the HDR really shines on the XDR. I could not see certain details on my older iMac 5K of various space craft tools and decorations. You can see the copper wiring on Iron Man's helmet near the eye-plate.
You are nearly blinded the moment before Captain Marvel appeared, but HDR10 allows the viewer to still see clearly the sun spot, the immediate lit areas plus the darker parts of the scene. In this way, the XDR is better IMO than the best OLED large screens out there from LG and Sony. I have the latest 77" LG OLED C9 and the Apple XDR beats it with the contrast and accuracy.
At 5 bars of brightness, it is comfortable. 6 is ideal for HDR movie viewing. The internal Mac Pro speakers is ok for dramas but something like Endgame requires at the minimum a nice 2.1 audio system.
Lastly, I find Apple's TV App plays HDR and HDR10 content better than VLC. IMO
Later