>>718229269
So, again, I'll say that RenoDX is outputting the "correct" image. But it's outputting an image in "HDR" format (or, if you want to be specific, a Rec2100PQ image). But somewhere along the way, Windows is receiving this data, but it thinks it's only sRGB.

This is what happens when I take the image file you posted, tell Blender it's a Rec2100 image, then tell it to output to sRGB. Looks a lot more normal. Not perfect, since the "source" image was only 8 bits, but it looks a lot more like you would expect. And on my side, I even get some highlights on the rocks and the fire.

In a game with proper implementation, you'd get something far more like what I posted. However, if you intercepted the signal, and pasted it into a program that just assumes everything is sRGB, the image you posted is what you would get. So what's happening is that RenoDX is "forming" an HDR image, but the game is not properly signalling that it's an HDR image when it sends it to the Windows compositor. So Windows just assumes it's an SDR image. Even if you have HDR enabled and Windows is sending HDR signal to the monitor.
It's like if you're trying to measure a long object with a yardstick, and you say it's "60% of a yardstick", but the game forgets the "of a yardstick" part and Windows just assumes you're talking about a footruler, so converts your measurement incorrectly to be "60% of a footruler". But since the monitor is expecting everything in HDR, it converts the incorrect conversion into yardsticks again and now you get "20% of a yardstick" being displayed to you.