This original post will continue to be updated with more information we learn as 3080/3090's get into the hands of gamers who have 4K@120hz monitors.  It started with the LG OLED CX, but I think it's best to open it up to any good information people have to share and may help the community.  The key here is the 4K@120hz,  60hz is half the bandwidth and won't experience any of the challenges.
 
General suggestions for any 4K@120hz users:

1. You may need to cut out a rear slot divider from your case if it blocks airflow (Other cards also needed this done) it's because this is a dual slot card.
2. Default bios switch is set to stock, so I recommend flipping to OC for FTW3 users with duel bios
3. Updated to latest drivers, 456.71 fixed a lot of issues with stuck clock
4. Update Precision X1 to 1.1.0.11 which will also apply a firmware update (unless new cards are already coming updated)
5. HDMI cable needs to be 8K 48gbs supported or you will get issues.  Windows looks fine but stuck at 60hz, some games crap out i.e. RDR2 when maxed.  These are actually really hard to find. I went with one from Walmart - Monster 8K 15ft 48gbs platinum fiber optic HDMI for $45.00 and it does NOT work for everything so I DON'T Recommend this cable.  I have a monoprice 8K cable and so far it's doing everything. the issues I had with the monster cable are gone.
6. Set Windows Display capabilities - go into advanced display settings and set resolution to 3840 x 2160, you also have to set the monitor Refresh to 120hz (defaults to 30 or 60), and enable HDR, Enable Variable refresh rate, enable hardware-accelerated GPU scheduling (though this does rob a few cycles of the GPU)...  It's amazing none of this is on by default or auto-detected.  would be nice if LG offered a driver!
7. Set Nvidia Control Panel display settings - from the Nvidia control panel choose Change resolution, in section 2 - choose a resolution of "PC"  3840 x 2160, 120hz refresh. Section 3, override to NVIDIA color settings and choose 32-bit, 10 bpc, RGB, FULL. and apply
8. Set Nvidia Control Panel video playback settings - Nvidia Control panel, chose video\Adjust video color settings on left tree menu, then choose "with the NVIDIA settings", select the advanced tab, and choose "Full" so video's use the full black level HDR capabilities.
9. Set Nvidia Control Panel scaling option -in Nvidia control panel, choose Adjust desktop size & position from left tree menu,  for scaling it seems to look best when set to No scaling or aspect ratio, scale on display so it's all native signal to the TV and it handles any adjustments.
10. Set Nvidia Control Panel G-sync -in Nvidia control panel and all your games MUST have VSYNC off, or it will clamp it low, for me I had a few that were stuck at 60hz wth v-sync on, some let it go to 120, but locking v-sync on defeats the purpose of having G-sync.  Makes sure G-sync is enabled on your display as well!
11. If you have any trouble getting any settings to stick, there's a really high chance your problem is your HDMI cable not supporting a full 48gbs, I tried 4 different newer high quality cables that were 4K rated and NONE of them worked.

 
Suggestions for OLED CX, C9 users:

1. Update your TV Firmware to 03.11.25 or newer which fixes a few issues like g-sync flickering.  there is a 03.11.26 out there but it's for 55", 65" models only
2. For LG OLED TV specific settings.
   1. Set the HDMI input to Console (or PC) via the main home screen edit which supposedly is optimized for PC/Console.
   2. Under all settings \ picture, set aspect ration to 16:9, turn off energy savings,
   3. Under the additional settings make sure HDMI Ultra HD Deep color is enabled, Instant gaming response is enabled, turn off filmmaker mode auto change. 
   4. Under the Picture mode keep sharpness <10, any higher creates artificial film grain look.
   5. Under Advanced controls menu I turn off dynamic contrast, dynamic tone make to HGIG, Super resolution off, color gamut to auto. 
   6. Under Picture options menu I set black level to low, motion eye care to off.
   7. Under OLED screen saver menu, I leave on Screen Shift, but turn off Logo luminance Adjustment.
   8. Under the General \ AI Services - turn off AI Picture pro, AI brightness control and then under additional settings turn off power saving mode.

 
REQUEST from Community: We are finding that many issues are due to HDMI cables.  so we're going to get a listing going of what cables work and dont, so people know what to order and don't waste money or deal with frustration.  Please share your specific cables that are working or not working and I'll update the OP.  For it to be "Working" it means ZERO issues. every game works, windows runs 4K full color with 32-bit 10 bpc @ 120hz,  there is never any flicker, all games launch FULLSCREEN and run without issues, artifacts.
 
Signs of cable failure: Unable to reach full windows resolution @ 120hz, games only run in windowed/borderless but not full screen, there is flickering or occasional black screens, games crash or failing to start. Some games worked fine, but most have trouble, like SW Battlefront II won't go into full screen, RDR2 crashes on anything over 2560 res, Death Stranding had some visual artifacts and at one point screen went green & pink. other games were not getting over 60 FPS when I know it can. 
 
Working:

• Monoprice DynamicView Ultra 8K Premium High Speed HDMI Cable, 48Gbps, 8K, Dynamic HDR, eARC, 6ft Black - Product # 31231 - confirmed on LG CX with 3090
• Belkin HDMI Ultra High Speed - Product # AV10176bt1M-BLK or AV10175bt2M-BLK - confirmed on LG CX with 3090
• AudioQuest Pearl 5' 8K-10K 48Gbps HDMI Cable (From Best Buy)

 
Partially Working:  (meaning it appears to be working, but there may be an anomaly you are not sure it's 100%)

• Monoprice 138627 Ultra High Speed HDMI Cable - 30 Feet - Black, 8K@120Hz, Dynamic HDR, 48Gbps, Fiber Optic
  • Workaround is to turn "Instant Game Response" mode OFF and then back ON before playing a game to get G-sync to work properly, everything else works perfectly fine.  This is the only known long optical cable found that works.  this was with LG OLED, so it's possibly issue with IGR/Firmware of the TV and not the cable.

 
Failed:

• Monster UHD Platinum Fiber Optic HDMI Cable - 15ft - VIPRB-HDMI700HD4M 
  • Full Screen RDR2 fails on Vulkan, Tomb Raider Crashes at launch.
• AmazonBasics Nylon-Braided 4K, 18Gbps HDMI to HDMI Cable, 10 Feet
  • No 4K 120hz Desktop resolution, no games run 4K
• 4K HDMI Cable 10 ft - Atevon High Speed 18Gbps HDMI 2.0 Cable - HDCP 2.2-4K HDR, 3D, UHD 2160P, 1080P, Ethernet - 28AWG Braided
  • No 4K 120hz Desktop resolution, no games run 4K
• Twisted Veins HDMI Cable 8 ft, 2-Pack, Premium HDMI Cord Type High Speed with Ethernet, Supports HDMI 2.0b 4K 60hz HDR
  • No 4K 120hz Desktop resolution, no games run 4K
• Generic HDMI cables
  • Mixed results but none of them worked for games, only a few let windows run 120hz.

Another 3090 FTW3 owner stated that the Studio version of the drivers worked for them, but the GRD (game ready drivers) were causing issues like you are describing. He did state that he was getting an audio buzz with the Studio drivers, though.

What temps are you getting with the OC bios switch on?

Like the poster above me said, I don't think you can get full specs out of the oled with these cards yet.  But LG did officially say they are working on a firmware update.

I don’t own a CX, but watched a setup video.  There is a specific display mode meant for PC.  Did you try this?  Maybe that’s why you had to make so many manual adjustments.

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

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).

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
 
 

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

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. 

That would add a pretty serious amount of input lag to this display. I've found that the black screen flickering is caused by gsync, which is broken on a lot of 'gsync compatible' displays. Just disable gsync for the time being. It's being working near flawlessly for me. 

Did you have to get the new firmware to get g-sync working?

I just find it incredible that there are so many people on here who were able to purchase the FTW3 Ultra 3090 - I can't find a SINGLE GPU for sale anywhere. How on earth did these guys get it?
 
This is the most frustrating product launch ever.

Awesome info Bettc! 

Baasha
I just find it incredible that there are so many people on here who were able to purchase the FTW3 Ultra 3090 - I can't find a SINGLE GPU for sale anywhere. How on earth did these guys get it?
 
This is the most frustrating product launch ever.

Bud you are not the only one. I am soooo frustrated.