Kobo not showing up in devices on Digital Editions.

Hi there. So my Mum uses a Kobo ereader for library book and she loads them through digital editions and has done so for a long time. We recently updated to computer to Mac OS Catalina and then updated digital editions to the lastest version (4.5 I think). However, when plugging the kobo into the computer it doesn't show up in devices of digital editions, although it does show up on the desktop. Have tried reinstalling DE with no luck. Ant suggestions? Cheers.