The solution that works for me.

I created new SSH key using the command, ssh-keygen -t rsa -b 4096 -C "[email protected]"

then; ls -l /home/user-dir/.ssh/

here you will see two pub keys. One is an 'id_rsa.pub' file. it is not the key. and another is there with 'id_edxxxx.pub' this is the github sshkey. cat it and copy to your github environment for use.