black screen at boot

RyeinI've had exactly the same problem and I can totally understand your frustration.Kam didn't help at all as well. For you it is too late already but I did manage to get it fixed without resetting or reinstalling windows.

So for any future readers, the fix is to install a remote desktop application (in my case AnyDesk), boot the pc and when your monitor is black just log in to the pc using the remote desktop application from another device (in my case Anydesk on Android). Then go to settings, system, display and there you can turn off the toggle for HDR and your screen will work again!