Sometimes, NCP will not show proper monitor information. This is because Windows gets confused and gives the wrong settings in the display settings. It's a pain. Go into monitor settings in Windows settings first, make sure that the refresh rate, resolution, etc. all show proper info. Usually you can change them as needed (I was able to with my U8G). Then go into Nvidia Control Panel and if you had to make changes in Windows, those changes will be visible in NCP now. Double check your color depth, etc. as well.

Not sure the riser cable would matter but I'd install the new one anyway.

Enhanced HDMI is under the TV's first menu selection. It's called HDMI Format > Enhanced format.

Here's the cable I'm using, btw:

https://www.amazon.com/gp/product/B08KSY32VR/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

I couch game with my PC. I'm using the 55U8G and playing at 4K, 120hz, HDR, HDMI to TV, eARC to receiver, etc. I push the system as much as I can with the TV and it's been a great experience. Also, there was a commentor on Rtings who had a great baseline for the calibration setup of the various picture modes. If you want to go further, you can use something like a Color Munki and DisplayCal.

Hope this info can help you.