2070 Super has an HDMI 2.0b spec port, which is good to 4k @ 60hz. I wonder if you aren't getting some weirdness by trying to go out of spec with it.

Are you actually getting 4k120hz at the desktop? And then in the game it's weird?

Also, the Windows Settings and the Nvidia Settings change the same configuration-- you shouldn't have to make them 'match', but sometimes Windows is weird and won't let you do something Nvidia will, or vice versa.

I also had some weirdness (HDR was available, but then I wouldn't get ANYTHING on the screen when I tried to switch it on at the TV (it's in the menus somewhere, called Deep Color, I think)), but switching modes (Standard, Game, Sports) would reset things so then it did work.

For your issue... I'd try knocking it down to 4k60hz and seeing how that works--I know it's not ideal. If you can narrow it down to being an HDMI 2.0b issue, try a DisplayPort 1.4 > HDMI 2.1 adapter-- https://www.amazon.com/Cable-Matters-102101-BLK-Computer-Adapter/dp/B08XFSLWQF

Also, make sure the cable you use is HDMI 2.1 (might say 8k 60hz / 4k 120hz on it). And don't make it too long a cable, or at least test it with something <10'. If it works good like that and you are having trouble with long cables, but you still need the length, I've had good luck with optical HDMI. They're a little more expensive... but I paid $65 for 65' here: https://www.amazon.com/gp/product/B0923WRVY7

Good luck!