This has to do with the overlayFS is what Docker uses, and Docker does not work (natively) on OpenBSD.
To make Docker work on OpenBSD there has to be a VM/VMD running with Alpine that runs Docker. Performance may be flakey but i can always try to make that working.
Right now the Golang version on OpenBSD struggles with
./fake_shell_overlayfs.go:290:15: undefined: unix.Mount
./fake_shell_overlayfs.go:306:45: undefined: syscall.MNT_DETACH
This has to do with the overlayFS is what Docker uses, and Docker does not work (natively) on OpenBSD.
To make Docker work on OpenBSD there has to be a VM/VMD running with Alpine that runs Docker. Performance may be flakey but i can always try to make that working.
I'll keep you updated with that project.