Can't connect Kobo e-reader with Adobe Digital Edition via iMac anymore

When I connect my Kobo Auro e-reader (version 4.12.12111) with my i-Mac (macOS Mojave 10.14.2), it looks on the e-reader that it is connected but in Finder I don't see the e-reader and it is also not visible in system/hardware/usb. So disconnecting the e-reader isn't also possible.

What to do, to make a proper connection between iMac and e-reader?