In case you want to just have an encrypted SSH key with password in keychain, you can make it work automatically when logged in (and when Mac is unlocked) by putting in .ssh/config:

  Host github.com
    AddKeysToAgent yes
    UseKeychain yes
    IdentityFile ~/.ssh/id_ed25519

Docs: https://docs.github.com/en/authentication/connecting-to-gith...