We have used cioverlay on previous combinations of platform/video card and OS. However, with the latest Z2/Quadro P620/RHEL8 this no longer functions.
Installed driver using specifics in https://developer.nvidia.com/blog/streamlining-nvidia-driver-deployment-on-rhel-8-with-modularity-streams/ [this apparently automates all the previous run level 3 (or multi-user.target) and disable nouveau steps].
All is good at this point and utilities indicate the nvidia driver is in use.
running nvidia-xconfig --cioverlay and a reboot results in a black screen.
Similar outcome using the manual steps and running NVIDIA-Linux-x86_64-.run
AFAIK, CIOverlay requires the composition extension to be disabled which doesn’t work with gnome3 so you will have to use a different DM/DE.