This same process is true for Gitlab, Github, Bitbucket, etc.
If you have more than about 5 SSH keys on your PC in
~/.ssh/, you need to setup your
~/.ssh/config file so that SSH to github.com (or other SSH server) uses the correct SSH Public Key the first connect try.
add this to
Host github.com Hostname github.com User git Port 22 IdentitiesOnly yes PubKeyAuthentication yes IdentityFile ~/.ssh/mygit
mygitis the key you created following the process (without ssh-agent).