Louis Abel via rocky writes:
Converting from a CentOS 8 system with secure boot to Rocky Linux 8 should "just work" while leaving secure boot enabled. I would recommend using the script that is provided here:
https://github.com/rocky-linux/rocky-tools/tree/main/migrate2rocky
I have tried the migration, and it failed completely, but it's unrelated to secure boot.
The process failed at the point where it tries to install the large bulk of packages downloaded. The reason was: a lot of packages are installed in both i686 and x86_64 form, e.g. -devel rpms. dnf then complained about a file (IIRC, a man page) that is owned by two packages. It was either libgpg-error or libgcrypt -devel, I don't remember which, and I'm nearly sure it doesn't matter which.
After that, the package list on the system was inconsistent as some rocky rpms were already installed. The migration script refused to do anything meaningful afterwards and I had to reinstall from scratch and restore the data backup.
Secure boot was not a problem, I had to disable it for PXE and re-enabled it after installation.