I have an Odyssey G9 running at 240Hz which I absolutely love. I finally was able to order my dream card (3090 FTW3 Ultra Gaming) from EVGA's website and I installed it into my computer last night. It booted fine first time and when I plugged in my display port cable (special one came with Odyssey G9) it showed a very low resolution and then gave no signal notification. When I plugged in my other monitors they worked with no issues. Then in NVIDIA Control Panel I lowered my Frame Rate on the Odyssey G9 to 120Hz from 240Hz and the screen began to work. For information purposes, I upgraded from an EVGA 2080Ti FTW3 Ultra Gaming and updated my drivers on NVIDIA GeForce Experience. Anyone know anything I can do to be able to run my Odyssey G9 at 240Hz again with the 3090?
 
CPU: Intel I9-9900K @ 4.7GHz
GPU: EVGA 3090 FTW3 Ultra Gaming
RAM: GSkillz Trident (4x8GB)
PSU: Corsair AXi 1000W
Motherboard: Gigabyte Aorus Pro Wifi

SprayingMango
The Samsung displays are known to be problematic, they do not have G-Sync modules in them and have severe flickering issues and quality control issues. There is a class action lawsuit out there for them.  
 
You should also use DDU to do a full clean driver install. 

Upon doing some more digging I've found a driver update to be loaded on the monitor via USB that addresses a number of issues regarding 3090/3080 cards. Hopefully this will yield some results and I will report back the results. 
 
In the case that this does not fix this issue, what is DDU used fix? I am unacquainted with the program but any potential solution is worth a try!
 
Thank you for the help!

sarchbell
Upon updating the Odyssey G9’s firmware to 1008.1 I was able to run at 240Hz. Unfortunately a blue flicker appear in some applications so turning G-Sync off promptly fixed this issue. Thanks everyone for your help!

this is why i returned it.  i will not be "turning gsync off" on a $1500 gsync "compatible" monitor.  I really think that gsync ultimate is the way to go.