With Docker Desktop for Mac, its finally possible to forward the ssh agents from the host through to a container. Wooohooo.
But. If you are accessing the Mac itself via ssh, then any ssh identities that are forwarded cannot be forwarded into the container.
Eg, I was on Linux, ssh'ing to the mac and trying to bring up the docker containers with the identity. It doesn't work, couldn't get the identities to come through.