echo use-standard-socket >> ~/.gnupg/gpg-agent.conf
echo enable-ssh-support >> ~/.gnupg/gpg-agent.conf
$ echo $SSH_AUTH_SOCK
/run/user/1000/gnupg/S.gpg-agent.ssh
$ gpgconf --list-dirs agent-ssh-socket
/run/user/1000/gnupg/S.gpg-agent.ssh
$ systemctl --user show-environment | grep SSH_AUTH_SOCK
SSH_AUTH_SOCK=/run/user/1000/gnupg/S.gpg-agent.ssh