Comment 1 for bug 1928563

Probably related to https://bugs.launchpad.net/cloud-images/+bug/1873506 too.

Alternative solution:
Put in documentation of the image https://app.vagrantup.com/ubuntu/boxes/focal64 some indication that, for Virtualbox to properly display with 3D acceleration and with sound, one needs to add:
sudo apt install linux-image-generic