Ok, pas réponse mais ma solution en espérant que cela puisse servir à d'autres ;)
Hello,The solution to my issue.Matek's service was poor and the guy was giving random answers instead of really trying to understand the problem.Then when I tried to use the warranty, the response wasn't even polite ...I'm pretty disappointed because I really think Matek boards are good. (but the service has a huge margin for improvement ...)The real problem: broken, poorly soldered USB pinsthe USB is connected to the board by 4 pins.Vcc = was okD + :?RE-:?ground = was ok=> so everything was fine because the board was powered on, but obviously I was not able to communicate with it.So cut a standard USB cable and solder it to the board ... and surprise it worked.be careful, the pins are very small and the solders will break easily.Second step, once you are connected to the board, you need to flash it.then reconnect and go to the "ports" page and put UART 1 on MSP (you can also keep USB VCP)Last step:buy a 6PIN USB to TTL UART module (CP2102) and you will be able to connect to the board even if the USB is broken:* Vcc => 5 v* Earth => Earth* Rx => TX1* Tx => RX1Ok that's it ... Now let's try to fix this USB connection correctly.