1. Generate an SSH Key Pair

Windows/Linux: ssh-keygen
It's recomended to set a password as this will encrypt the Private Key.

  1. Place the Public Key on the Linux Server

Paste the contents on the Public Key into the authorized_keys file.

sudo nano ${HOME}/.ssh/authorized_keys

  1. Restart SSH
    sudo service sshd restart

Connect via SSH

Terminal: $ sudo ssh -i path-to-private-key username@remote-server-ip

Termius Docs
Putty (Ionos Tutorial)

Disable Password Authentication

sudo nano /etc/ssh/sshd_config

Uncomment PasswordAuthentication yes

Then set value to no PasswordAuthentication no