An issue has been discovered in the GRUB2 update that prevents booting

Some users of RHEL 8 and CentOS 8 have encountered issues issues after installing yesterday's GRUB2 bootloader update which fixes critical vulnerability. The problems manifest as an inability to boot after the update, including on systems without UEFI Secure Boot.

On some systems (for example, HPE ProLiant XL230k Gen1 without UEFI Secure Boot), the issue occurs even on a freshly installed minimal configuration of RHEL 8.2. After updating packages and rebooting, hanging occurs and the GRUB menu is not displayed.

Similar boot issues are noted for RHEL 7 and CentOS 7, as well as for Ubuntu and Debian. Users are advised to hold off on installing GRUB2-related updates until the situation is clarified; if boot issues arise after the update, they should roll back to the previous version of the GRUB2 package using a recovery boot medium.

Source: opennet.ru