RHEL 9 /boot/grub2/grub.cfg file must be group-owned by root. GROUP ID: V-257790 RULE ID: SV-257790r991589 The "root" group is a highly privileged group. Furthermore, the group-owner of this file should not have any access privileges anyway.
Solution
Change the group of the file /boot/grub2/grub.cfg to root by running the following command: $ sudo chgrp root /boot/grub2/grub.cfg