Explanation
To disable root login over SSH, the server administrator needs to edit the SSH configuration file located at
/etc/ssh/sshd_config. This file contains various settings for the SSH daemon that runs on the server and accepts incoming SSH connections. The administrator needs to find the line that says PermitRootLogin and change it to no or comment it out with a # symbol. Then, the administrator needs to restart the SSH service for the changes to take effect. References:
https://www.howtogeek.com/828538/how-and-why-to-disable-root-login-over-ssh-on-linux/