How to setup Port Forwarding set up with Ethernet connected devices - Not Listed in Mobile App Drop Down of Attached Devices

We have a XB7 gateway that we trying to setup port forwarding for an attached ethernet device.  The device is a Synology NAS (network access storage).  It is attached directly to the Gateway.  The device has full internet access and is working properly.  But we want to setup a specific port forward for another service.

When we go to the port forwarding in the mobile app, the drop down list of connected devices only lists WiFi devices.  It does not list any ethernet devices,  I have other devices also connected and they are not listed. This is even though the attached Synology NAS is connected directly to the XB7 Gateway.

Under older Xfinity/Comcast Gateways, the devices would show in the website control panel.  Alternatively, we could type in the local network IP address and port, to setup port forwarding via the same desktop / website tool.  Now that we must select from a drop down menu in the mobile app and we cannot setup the port forward.

Please advise how we can make this work.