Thank you for your help. I can see the link in the dialog now - missed it because it just looked like text.
As pointed out in the wiki https://wiki.seeedstudio.com/Wio_LTE_Cat.1/ you cannot use the Arduino IDE’s serial monitor, but rather need to use a third party serial terminal. If you use the IDE serial then you need to open and close the IDE each time you switch between bootloader and virtual com port modes.