I clearly have some learning to do on HDR, no matter MS can't fic their ****. I'm very happy with the graphics I get in Edge with my settings even if its not setting the Asus to HDR, I currently do not have any of the issues that irritated me for months.
Now, my COD, when I start the game (it enables the Windows HDR automatically and I get the Asus screen message popup saying HDR enabled and its changing some other stuff). When I alt-tab to the desktop everything in Windows look **** as before. When I exit the game, it automatically disables Windows HDR and my desktop is looking good again. So basically what it looks like is the games will enable the Windows HDR and disable it again so you don't need to.
So for me I think I found my sweet spot until we eventually get a fix. I'm sad this is not working for you mate, I really tried my best to find that for you.
My COD is "Modern Warfare III"