Cube orange connection problem with QGround

I downloaded the latest version from QGroundcontrol.com but the orange cube is not connecting to qgroundcontrol via usb.

I can connect MP via usb but not qgroundcontrol

do you have any ideas? what can I do??

Update: this problem only occurs when ardupilot firmware is installed. When I install the px4 firmware, it connects with a usb cable without any problems.