After a crash during an update (which I managed to recover from), the default file manager Nautilus no longer works, and crashes so hard it crashes VirtualBox too.
I tried by deleting it then reinstalling it, but didn’t change this behavior. Also there’s a non-zero possibility that the original crash was caused by Nautilus itself.
Have you tried reinstalling the guest tools?
Or Nautilus, or related subsystems like the display manager?