This guide will explain how to set up a [VirtualBox][] VM running [Ubuntu 20.04][] and, using the new [autoinstall][] tool and cloud-init, install OpenSSH server, add a group and a user, who can then connect to the machine via SSH. This was done on a 2016 MacBook Pro running macOS 10.15 "Catalina" and VirtualBox 6.1.6 (with the VirtualBox Guest Additions installed).
You will also need a group name, a username, a password hash and an SSH key pair.