NVidia driver 520.61.05 / Cuda 11.8 / RTX 3090 = black display and superslow modesets

I have the same problem, and found it a little hard to revert to the old version. Here are the command that saved me:

sudo apt-get purge nvidia*
sudo apt-get install cuda=11.7.1-1 cuda-drivers=515.65.07-1 libcudnn8-dev=8.5.0.96-1+cuda11.7 libcudnn8=8.5.0.96-1+cuda11.7

I found some help in that post:

The key to find the old version name is to use “apt list -a cuda”, “apt list -a libcudnn8”.