RK Royal Kludge R75 (ISO German) not recognized

[be-bu]

The Royal Kludge RK75 (germany) won't be recognized from the web tool, neither via usb cable or dongle. I even tried the offline app and this won't recognize the keyboard as well.
I get asked to authorize the device i want to use, select either the dongle or the keyboard directly and afterwards nothing happens. The tester just works, but I can't edit my keyboard and only see the rocking via-icon.
Issue appears on macOS 15.2/15.3 with Chrome (Version 132.0.6834.160) and Edge ( Version 132.0.2957.140 ) and Windows 11 likewise.