Could be due to this: Rocky 8.6 host, Rocky 9.0 guest? - #2 by jlehtone
Check if sse4* is accessible in the cpu on your Rocky Linux 8.x install, so:
cat /proc/cpuinfo | grep -i sse4
if you get zero results, that means VirtualBox is not passing through the functionality that allows RHEL9 and Rocky9 to work.
More info on that here: RHEL9 Raises Base Target For x86_64 CPUs Plus Possible Optimized Libraries With glibc-hwcaps - Phoronix
And here for virtualbox: virtualbox.org • View topic - Kernel Panic - Centos 9 Stream
Red Hat: New installation of RHEL 9.0: Kernel Panic Fatal Exception - Red Hat Customer Portal