Also, for anyone that has run a Focal or Groovy box, and had it hang completely with it not showing up in Virtualbox GUI for stopping, the following can get the image unlocked for future work (without a reboot)
vboxmanage startvm <UUID or name> --type emergencystop
vboxmanage unregistervm <UUID or name>
If you're unsure of a UUID or name, try running a Vagrant command (such as vagrant halt). If it fails, Vagrant will print the command used which includes the UUID.
Also, for anyone that has run a Focal or Groovy box, and had it hang completely with it not showing up in Virtualbox GUI for stopping, the following can get the image unlocked for future work (without a reboot)
vboxmanage startvm <UUID or name> --type emergencystop
vboxmanage unregistervm <UUID or name>
If you're unsure of a UUID or name, try running a Vagrant command (such as vagrant halt). If it fails, Vagrant will print the command used which includes the UUID.