I don’t think flyctl will work with Windows 7. We need support for this, which I’m fairly sure only arrived in Windows 10: AF_UNIX comes to Windows - Windows Command Line
There might be a way to use Wireguard to setup the private network connection and bypass our agent to get around this specific problem. You’ll need to fly wg create, follow the instructions to configure wireguard, then set an environment variable FLY_REMOTE_BUILDER_HOST_WG=true.