The device is not recognized anymore. It was during several months and from now on, it isn't. But, as the current sketch creates a BLE connection, the device is recognized with Bluetooth. So it seems that's only a problem of USB connection with the computer.
The important point is there is no driver for the device In the Windows device manager. Previously, it should be one.
The board 'Arduino megaAVR boards' is included in Arduino IDE. There was no change in Arduino configuration except I removed some unused libraries.
Please help me. Where is and what is the missing driver?
At the present time, the device appears in the section 'Other devices' as well as in the Ports section ('mEDBG Virtual COM Port (COM10)') as a hidden device because it's considered as not connected to the computer. But it is, and I tried 2 USB cables with the same result.
In order to make all relevant information available to any who are interested in this subject, I'll share a link to the issue report @anon70927101 submitted here:
Finally, the Arduino support proposes a replacement of the board.
As the board is working normally except the upload, I think that the problem is probably due to the USB port of the board. Another board is working normally with the same usb port of the computer.