HDR will enable with 8, 10, or 12 bit color. Have you tried to reinstall your graphics drivers to see if that might help you get a 10 bit option?

What TV do you have? Sounds like you might not be using an input port that supports HDR. Setting the bit depth in Nvidia control panel is not the same thing as HDR.

FWIW, I can't select anything other than 8 bit with Chroma 4:4:4 subsampling, and 8 bit or 12 bit with Chroma 4:2:0. (GTX 1080 Ti, it's been like that for over half a year)
 
Now, with Chroma 4:2:2 you should be able to select 8, 10, or 12 bit because I can.
 
Also FWIW, RGB looks better on my KS8000 than any Chroma subsampling with ANY text, and along with mouse movements (slight lag with Chroma).

I understand that you can select 422 and select 10 bit. This is not what I am trying to do, as it washes out colors horribly for me. At 30hz, I should be able to select 8 to 12 bit INCLUDING 10 bit on any color format. Why can't I? I'm not sure. 30hz and under supports 12 bit, but I can't select 10 bit which doesn't make any sense since 12 bit is MORE demanding than 10 bit. Again, I am selecting 30hz and using HDMI.

Do you have HDMI ULTRA HD Deep Color activated on the port you are connecting to? Do you have that port icon also labeled as PC?
 
But like I said earlier, 10 bit color in the Nvidia control panel doesn't really have anything to do with HDR. You need to enable the setting in Windows. Here is a good article from MS covering how to do that and use dxdiag to get more info about your GPU and monitor capabilities: https://support.microsoft.com/en-us/help/4040263/windows-10-hdr-advanced-color-settings
 
Also note your display support 4k 60 Hz 4:4:4 with 8 bit HDR in an HDR gaming mode that has less input lag, that's probably the best way to go unless you can't get over 30 FPS in game. More details on the modes here: https://www.rtings.com/tv...c6-oled#comparison_200
 
For what it's worth, I have the same behavior as you regarding only 8 and 12 bit showing on my LG @ 4k 30 Hz but I can use HDR properly at 4k 60 Hz RGB just by enabling the option in the Windows control panel. Though I do not keep it enabled for the desktop, games will have a separate in game HDR option you can enable; but it's an easy way to test. Turning it on for the desktop is needed to stream HDR video from the likes of Youtube, for games it's not.