Adding LTE modem interface to FreedomBox

I set up FreedomBox on my Raspberry Pi on Raspbian, with an LTE hat using RNDIS protocol. (Only found FreedomBox a few days ago and it is amazing!)

On the command line I can see usb0 interface up and working, but it is not shown in the network menu of FreedomBox. When I try to add a new interface it only shows eth0 to select.

Is there a trick to get also the the USB modem interface visible in FreedomBox?