Ubuntu 18.04 LTS
Oracle VirtualBox 7.0.2

I use old Ubuntu 18.04 LTS occasionally for GR-GSM, Fissure...
I updated VirtualBox 6.1.38 to version 7.0.2 and started Ubuntu 18.04 LTS guest OS and installed Ubuntu VirtualBox Guest Additions 7.0.2 and restarted guest OS. Result:
Kernel Panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)

I powered off the VM env and started guest OS to CRUB
inttx.jpg

and selected *Advanced options for Ubuntu and selected kernel x.128.

inttx3.jpg

After updating initramfs the guest OS started ok.