If you run with -vv during auth there's some debug text to do with cryptography selection. In the case of github the response is: debug1: kex_input_ext_inf

If you run with -vv during auth there's some debug text to do with cryptography selection. In the case of github the response is: debug1: kex_input_ext_info: server-sig-algs=<ssh-ed25519-cert-v01@openssh.com,ecdsa-sha2-nistp521-cert-v01@openssh.com,ecdsa-sha2-nistp384-cert-v01@openssh.com,ecdsa-sha2-nistp256-cert-v01@openssh.com,rsa-sha2-512-cert-v01@openssh.com,rsa-sha2-256-cert-v01@openssh.com,ssh-rsa-cert-v01@openssh.com,ssh-dss-cert-v01@openssh.com,ssh-ed25519,ecdsa-sha2-nistp521,ecdsa-sha2-nistp384,ecdsa-sha2-nistp256,rsa-sha2-512,rsa-sha2-256,ssh-rsa,ssh-dss> Which suggests you'll be using rsa-sha2-256 with your client version, or absolutely nothing in the future if you're using one of the older releases such as on MacOS.