Usually this is because the kernel source is not installed, or at least not installed properly.
First, what I would do is find the kernel-source*.rpm package at Redhat's FTP site. Attempt to reinstall the nVidia kernel source rpm's afterwards.
I had to reinstall the kernel source manually after running the Redhat 8.0 update agent for the first time.
"Physics is like sex. Sure, it may give some practical results, but that's not why we do it." - Richard P. Feynman