tl;dr to move to the newer more secure format use ssh-keygen -o -p -f file_name such as: ssh-keygen -o -p -f ~/.ssh/id_rsa not necessary for ed25519 as

tl;dr to move to the newer more secure format use ssh-keygen -o -p -f file_name such as: ssh-keygen -o -p -f ~/.ssh/id_rsa not necessary for ed25519 as it can only be stored in the new format.