Nab yourself either a DP to HDMI 2.1 or USB-C to HDMI 2.1 box, and then update the firmware on the chipset when you get it. You'll be quite happy.
As for Dolby Vision - a few words of advice. Thus far, DV for gaming have been total rubbish on anything I've tested on either Series X or PC - even games like Halo Infinite that are suppose to use it natively, and not an auto HDR conversion. I highly recommend sticking to HDR10 for gaming, go watch Vincent @HDTVtest's videos on the topic.
For movies and tv however, DV encoding is absolutely amazing at preserving the artistic integrity and giving it that movie theater feel - however I am of the strong opinion that no Win PC application can hold a candle to running native smart apps on the TV itself, with access to low level API calls. They don't need to mess around with 3:2 pulldown, and seamlessly match the correct refresh rate for content (real 24hz for 24fps content), as well as a much more precise bfi engine. Netflix, Disney+, whatever - run it on the tv. For local media files, you can install Plex as a smart app and just setup the media server on your computer. This is also coming from a very long time user of media player classic and high end codecs. Even MadVR cannot match native app accuracy.
The adapters are hit and miss, I got a deconn one and it didnt work right
I switched to cable matters and it works great.
I use the Cable Matters 8K DP-to-HDMI adapter with my 6900XT and LG C1. After overriding the display's EDID, I'm able to achieve full-RGB at 4k@120hz albeit without VRR.
https://www.amazon.com/gp/aw/d/B08XFSLWQF
Modified EDID for LG C1 55" (all colorspaces except RGB are disabled): https://github.com/nvllsvm/dotfiles/blob/master/non-user/mars/lib/firmware/edid/office_tv_lg_c1_55.bin
Loading the EDID at boot: https://github.com/nvllsvm/dotfiles/blob/6b4c8ab2191dc98b52be3b0637da638378cf91ca/non-user/mars/boot/loader/entries/arch-zen.conf#L10
So, someone up in the comments suggested that people have been able to drive the display just fine with an adapter, excluding VRR only. Adapters such as this one, https://www.amazon.com/Cable-Matters-102101-BLK-Computer-Adapter/dp/B08XFSLWQF and that there's more info on that stuff in LTT Master Thread for G-Sync Compatible. So, I'll browse that a bit too and see what comes up.
As for the bandwidth, DP 1.4a meets all those demands, thus the other screens with the same panels inside from LG like ASUS, Gigabyte, and even LG UltraGear works just fine with all of that, including VRR. And it's all driven by DP 1.4a there, so we should be okay in regards to meeting the bandwidth demand.
Can you give a link to a few examples, like by CableMatters and others?
Is something like this is what you're thinking of? https://www.amazon.com/Cable-Matters-102101-BLK-Computer-Adapter/dp/B08XFSLWQF
I will take a look at LTT thread as well.
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!