If you are running cumulus OS, once you login with a private key, you should be able to create a user and add it to the sudoers group and depending on NCLU permission level, to the netshow (no changes) and netedit (changed permitted) groups. This is the standard debian (Linux) method to add users
I think there is the user “cumulus”, but when login the switch tells me that the “method” of access is with the private key. Maybe has not enabled both authentications methods.
In the config I see : cumulus no password or anything else