I checked the LG manual, in the resolutions section it states it supports 60Hz 4k only for VRR. 
 

Leftbase
Thank you for posting this - 48" CX user here and future 3090 owner...

I think alot of us appreciate the information.

Thank you for this update. I am looking to get both the 3090 and will be picking up a LG CX 55" around Black Friday (last year LG C9 had a pretty substantial discount, so holding out for that this year as well).

Alot of the newer tvs need a few firmware updates to get everything working properly particularly with these new cards

There is a new Game Ready Driver. Reddit is reporting majority of their issues are fixed, even weird clock locking. 

Driver: https://www.nvidia.com/Download/driverResults.aspx/164741/en-us

Reddit: https://www.reddit.com/r/nvidia/comments/j1ccfq/game_ready_driver_45655_faqdiscussion
 
 

On It now! thanks, will check it out.. looks like LG posted the firmware for older C9 models and the CX should be coming this week.. so combined with my new fiber optic HDMI cable coming tomorrow I am really excited to see how this card rips!

Wanted to add for anyone experiencing black screen flickering that disabling "instant game response" on my LG CX solved the issue in all games I tried to run at 4k 120hz. 

I watched Vincent at HDTVtest and he said he is working with Nvidia to fix the CX Gsync and subsampling issues @ 4K 120hrz 4:4:4.  Hopefully they can get it all dialed in as the TV is advertised to do so.
 
Question - How do you enable VRR on the CX, I only see Freesync Premium, or do you mean select auto game mode?

Kalvus1
Wanted to add for anyone experiencing black screen flickering that disabling "instant game response" on my LG CX solved the issue in all games I tried to run at 4k 120hz. 

thanks for sharing

Not sure why you're setting color to 12-bit instead of 10-bit. The CX's HDMI 2.1 ports are only 40Gbps bandwidth which means it can't do 12-bit. The C9's HDMI 2.1 ports are full 48Gbps bandwidth and can do 12-bit. But even then, neither the 2019 nor the 2020 OLED models have 12-bit panels, they are both 10-bit panels. Although some C9 users have stated that they get less color banding when running in 12-bit mode.