After struggling with this for a few minutes, I came across these steps which made it so simple...
From LOCALHOST (not logged in via SSH):
- ssh-copy-id -i ~/.ssh/id_rsa.pub [email protected]
Pess Enter for the options on "ssh-keygen", and replace "192.168.1.xxx" with your LibreELEC IP address.
Now you can turn off Password logins in LibreELE.