To start, your specs show a monitor at 144K.. Do you have a different one now?
I have the 3090 and do not have to run the system with CSM disabled. Since the CSM is involved in the Secure Boot situation, the only way it might tie in is with the Video cards firmware. Has it been updated lately? Many of those cards do get updates shortly after being released..
Does you monitor have any special capabilities, such as HDR? I will assume your Display port cable is up to the task and is not limiting in some way.
Do you have Thunderbolt enabled in the Bios?
The video output during boot is very basic so it should not be a problem with getting into the Bios. But maybe another monitor that had a DP connection would work.
If this card is an EVGA also, you may want to check over at their community site.
Edit: I also just saw this in case it might be involved
https://www.nvidia.com/en-us/geforce/forums/game-ready-drivers/13/454753/announcing-geforce-hotfix-d...
Maximus Z790 Hero,
Intel i9-13900k
Intel BE200