Hey I had this exact issue so I’d like to share how I solved this issue
For me it was SecureBoot didn’t allow nvidia driver to be loaded
Temporary solution would be to disable secureboot
For this, you need to enter UEFI configuration screen on boot.
For my machine, I needed to press F10 key while HP startup logo showed, but it depends on computer, so I recommend looking up maintenance manual for your computer online (it’s how I found F10)
After disabling SecureBoot, check if nvidia-smi outputs normally (as opposed to failed to blabla)
If it still fails, then it’s not signing issue so you need other solutions
For me it worked.
But UnrealEditor 5.6.0 still showed that error message. So this was no longer driver issue, it was the Unreal issue. So what I did was I downloaded UnrealEditor 5.5.3 (From the forum posts it seems that 5.6.0 has similar issue and people went back to 5.5.3 to solve their problems)
After that I enabled Secureboot again, but before that, I signed the key of nvidia driver so that SecureBoot will allow NVidia driver to be loaded.
I ran modinfo nvidia which showed that nvidia module was signed by dkms module signing key
I could find the key at /var/lib/dkms/mok.pub
and I ran sudo mokutil --import /var/lib/dkms/mok.pub to register the key, and then enabled the SecureBoot back on, and then everything worked normally.
I also did not install driver via .run file at for example https://www.nvidia.com/en-us/drivers/details/249194/
That’s a last resort option, and more preferably you should follow the instructions at https://docs.nvidia.com/datacenter/tesla/driver-installation-guide/index.html#red-hat-enterprise-linux
I followed the instructions for RHEL but there’s also Ubuntu and most popular Linux distros. Hope this fixes your problem