cannot boot (grub error)

[theoneandonly-vector]

I disabled secure boot (as it's not yet available) but I wasn't able to boot yet.

this command fixed it:
grub2-mkconfig --output=/boot/efi/EFI/rocky/grub.cfg

I found it here:
https://forums.rockylinux.org/t/solved-grub-prompt-after-centos-8-rl8-migration/2578

[ispringle]

I'm testing a migration from Centos8 at the moment. The first attempt would not reboot and was throwing an error with Grub/bootloader, subsequent restarts of that machine did not do anything new. I deleted that VM and tried again, running this command after the migration completed. The initial reboot failed but the second reboot worked as expected. Just adding this in case anyone else stumbles upon this same issue.

[komitov]

#162 should be able to fix this and it looks like it helped #163

[sla-te]

I have the same problem, though I wonder how you ran grub2-mkconfig for me its not a valid command in the rescue shell.