I don't know why freebsd lists things like this. It's confusing.
containerd is intended to be multiplatform from the start, so hopefully the FreeBSD support will come.
In theory, someone could create a Docker compatible engine using zfs, jails and virtual network adapters. FreeBSD can run Linux/ELF binaries (which is what the old Docker port did).
I've always felt like Docker for Mac/Windows was always a hack. Even the newer versions don't run natively, they just use the standard Win/Mac hypervisor API. On Win/Mac, you still have to VPN into your container network. On Linux, you can communication with containers directly via IP.
Am I mistaken? Am I mixing this up with something?
You can even connect to the console of the VM if you run into issues.
These version numbers are a little confusing because 11.3 now has newer ZFS features than the latest release from the 12.x branch and upgrading from 11.3 to 12.0 might cause issues as noted in the 11.3 Errata page.
Just because a dot-release of one major version was released, doesn't effect the other major versions also active.