thank you very much for your quick response!
Regarding the firmware, this totally makes sense. Thanks for pointing this out.
Yes, I tried option 3 and it says "ERR 100663404 Kartenfehler". I should have mentioned that above more clearly. Sorry for that.
The combination Windows & no Admin PIN leaves two options (2,3) which do not work for me (see first post for error messages).
The device is still recognized by the Nitrokey App - which worked fine regarding my regular encryption purpose by the way - unless I install the drivers generated by libusb. Then it does not work anymore. Otherwise, and that is the way it is at the moment, I am able to use the Nitrokey App and even decrypt the storage using the known User PIN. So this works fine!
But unfortunately I am not able to reset the Admin PIN to default. Is there another option left?