The VirtualBox Guest Additions are used to enable features in a virtual machine once installed. In normal cases, users will use the VBoxGuestAdditions.iso to install them, regardless of operating system.
For Rocky Linux and other Enterprise Linux derivatives, the guest additions can be installed via the CentOS Kmods SIG. Doing so allows the user to more easily maintain and use the guest additions features in their Enterprise Linux virtual machines.
To install the guest additions from the SIG, run the following:
# Install the release package
% dnf install centos-release-kmods
# Install the kmod, which will bring in the guest additions package
% dnf install kmod-vbox-guest-additions
# Reboot the system for it to take affect
% systemctl reboot
Once your VM is up, you can verify the service is running:
% systemctl status vboxclient
% lsmod | grep vboxguest