Hi, I am new to LXD containers , I had a little difficulty with the configuration of default profile .
I want when I create a new container in the container automatically added ssh key
The first post that you listed above, shows how to use cloud-init to set the SSH key.
The formatting of the profile is quite peculiar (YAML, follows the Python semantics) which helps if get familiarity with cloud-init in general.
When you run lxd init, you need to have zfsutils-linux installed. If you use the snap package of LXD, then the package is already supplied.
You can select either to create the ZFS pool in a file, or allocate it in a free partition.