Wow, looks like I may have a solution, following zero assistance from Dell support! Found tip on Internet, so I powered off laptop and disconnected USB C Hub from USB C port on laptop. I then powered back up and, when everything started, I plugged the USB Hub back into the USB C Port.  This immediately recognised the Ethernet capability and allowed me to set up an Ethernet connection again.  
I have recently bought a Dell Inspiron 5410 2-in-1 Laptop. I planned to use it with an internet connection through a USB hub, so I purchasd a Lemorele 8 in 1 USB C Hub, which I have plugged into one of the USB-C ports. During the first week of running, I was able to select an Ethernet connection, but I noticed that this would “drop” once or twice every day.  I switched back to using Wifi only until I could buy a new ethernet cable.  I have now installed this, but I can no longer find the ethernet capability on my laptop, which is running Windows 11.  Can anyone help me to get the Ethernet connection going? Many thanks - John
Configuring Ethernet connection on 5410 2-in-1