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.
It appears that you can only forward the local interactive users ssh identity, so on the Mac, make sure that the identity is present with ssd-add -K then bring up the docker containers and presto, there it is.
Not a huge issue, but spent some time figuring it out.
If you are still using workarounds for ssh keys, it might be time to switch.