VBox guest - dead after latest update

This may be related to the common issue here since the kernel module for VirtualBox is a 3rd party module.

If it is then following the steps in the workaround there should fix it.
The package name to remove would be kmod-VirtualBox-6.6.8-200.fc39.x86_64 if you are using the 6.6.8 kernel, or replace the kernel version with whatever kernel you are actually running. Then rebuild that module with the sudo akmods --force as shown in the workaround and VB should be back to functional after a reboot.