I have a Librem 15 v3 without a build-in Ethernet adapter, therefore I need to use an external USB to Ethernet adapter. That itself is not great. I hope there will be a mini-Ethernet adapter in the future.
The real problem starts when using QubesOS on the Librem 15 v3. The issue is that all USB ports are connected to a single USB controller. QubesOS allows to assign single devices to a Qube (VM). However, since all USB ports are connected to the same controller they are just one device from the perspective of QubesOS.
The solution @avog proposed, is to combine the USB Qube with the networking Qube.
That works, but it is not a good solution. The issue with the solution is, that now network and USB devices are handled by a single Qube. If you run into any issues with a USB device and you want to restart the USB-Network Qube, you have to power down all Qubes connected to the network. That is an issue.
I would prefer to have one USB port, which is on a separate USB controller. A controller which can be assigned to the networking Qube.
An even better solution would be to have a dedicated network card + Ethernet port build into the laptop. Then we would not need any adapters.