How to specify either aufs or overlay2 for Ubuntu 20.04

It is as easy as sudoing your nano at /etc/docker/daemon.json. I checked and for me this file didn’t yet exist. There was another .json file but not daemon.json. Then add the following clause:
{
 “storage-driver”: “aufs”
}

Or, if you prefer:

{
 “storage-driver”: “overlay2”
}

Save it and restart docker however you prefer. I use systemctl. If you do a docker info you’ll see that your preferred storage driver is now used. Enjoy the rest of your project.