How to make use of Plesk migrator on LightSail instances?

For many reason, we need to migrate out from LightSail for a specific server.

We built quite a lot on that instance over the years, and would like to take advantage of Plesk Migrator to retrieve our configuration. Unfortunately, it is required to be able to connect as a root user, from SSH.

As far as I know, LightSail provide a single "ubuntu" user able to SSH, and doesn't have root permissions. So that it seems impossible to take advantage of Plesk Migration.

What do you offer (apart from full backup)?

Thanks