I know that I have seen an Nvidia drivers tool kit hack to add possibility to install drivers when it not detects the current GPU but not sure if it will work for newer GPU !!!
I 'solved' my issue (for now) to go back to the 446.14 drivers.I'm glad that this issue is finally on investigation. I have the exact same problem but with a Geforce 1050Ti.
Have to restart MP after HDR content to get SDR colors back. Even the GUI colors are crushed until restart.
I'll keep an eye on your thread, and of course guys, I can do some test on my side.
Ho my god !I 'solved' my issue (for now) to go back to the 446.14 drivers.