Kernel upgrade on Rocky 8 reports a signature issue.
You will need to disable secure boot or read this page.
Sounds like “read this page” is the correct solution.
elrepo’s kernels are not SB-aware. You need to disable SB to install them.
The page says
In order to use ELRepo’s kernel modules (kmod packages) on a system with Secure Boot enabled, system administrators must import the ELRepo Secure Boot public key
So I don’t understand.
That is “kernel modules” (for RHEL kernels).
The kernel by ELRepo is a different thing.
You will need to disable secure boot, then. A maintainer in a previous reply in this thread has stated the kernels are not secure boot aware.

