Hi!
Its a very difficult subject to respond to and most dont have an hdr display so that’s why not many would reply 
Are you using the console commands manually instead of getting the game user settings through blueprint? Reason i ask because looking through the documentation it says:
“The Game User Settings controls will automatically clamp to the closest available match for the current output device and set all flags accordingly. Alternatively, you can use the following console variables to enable and change the available options for the HDR device and color gamut output needed.”
As im reading it seems when you use the console commands it is more of a manual input.
So you would need to manually set r.HDR.Display.OutputDevice and r.HDR.Display.ColorGamut.
I would suggest you try to do a blueprint setup as displayed in the documentation as it would automatically set certain flags and clamp to the closest available display match.
Hopefully this helps 