HDR on PC. "No hdr display detected"

So I just got a GTX 1070 and bought Horizon 4.
My Tv is a Vizio P65 and HDR is activated correctly in windows 10 and TV reports HDR10 in the info panel. I can definitely tell that the color space is HDR just by looking at the desktop colors so it does work.
Now, when I start up Horizon 4, TV still reports HDR10, image looks to be HDR but the video options for Brightness (in-game options) has 1 slider and says “No hdr display detected” .

So is HDR working on my setup or not? Signal is HDR for sure but maybe im not getting proper colors and rendering since the game says it doesnt detect a HDR display. Is is just an EDID issue??

Thanks for the help!