Settings, Display and Sound, Video Output, 4K TV Details. HDR should have green check mark next it. Install the Insects Demo from MS Store to test. It really shows the difference.
I have my XBox One X on HDMI Port 2.
1. Change Input to HDMI 2 (No Idea why but Mobile App or Menu will not do crap unless we are ON HDMI input we are trying to enable HDR on. Nothing has to be connected.
2. Menu, Input Settings, HDMI-2, Full UHD Color -> On. At this point we could also enable Full UHD Color with the Vizio Smart Cast Mobile App from the google play app store.
Do not change these setting while XBox One X is on or else screen will go black. Now turn on Xbox One X.
Problems:
Screen goes black intermittently with Full UHD Color On, even while playing NON-HDR Enabled games on XBox One X. Usually after playing for hours, so very rare. Cannot tell if TV or XBox One X is at fault.
Things to try:
1. Bought new cables. Still had problem.
2. Turn off UHD Color on Port 2. WORKS!
3. We will need to test a non-HDR device to the same port the Xbox is connected to when Full UHD is turned on within the menu. Turn Full UHD on with the Xbox connected, disconnect the Xbox and connect a non-HDR device to test.
4. XBox Support said to do a system reset on the XBox.