Enable SSH login by public key

Generate private key on your working machine

ssh-keygen -t rsa -b 4096 -C "your_email@domain.com"

And now copy public key to server by

ssh-copy-id user@server

Enter server password and done

Disable server login by password by update below values

ChallengeResponseAuthentication no
PasswordAuthentication no
UsePAM no

sudo systemctl reload ssh