I’ve been looking through the interface, but can’t find anything to shut / disable one of the four Ethernet ports or interfaces. Would seem to be a pretty basic functionality, so its probably there, just can’t find it.
You can’t disable the ports for now. But there’s a workaround: assign the ports you want to disable to a VLAN you don’t use (for example, X3). Then, enable the VLAN for a VPN client connection but don’t actually start the VPN connection.