I bought the board in February 2022.

As I wrote before I tried different ports, cables and computers without any effect.
The USB cable I use now was previously used for data transfer and it worked perfectly. So I'm sure it's a USB data cable.

I can't see any damage to the Duet's micro USB port. I also compared the USB port of the Duet with the micro USB port of a Raspberry pi, but can't find any differences.

The STATUS LED does not light up, blink or pulse when I connect the board to the computer. When I double tap the reset button nothing happens.

@jay_s_uk no matter what I do, neither a COM port nor a folder is displayed.
The only two things that work reliably are the 5V and 3.3V LEDs.

@droftarts I've already read that, but it can't be executed because I can't get a working connection to the board.

The Duet 3 mini 5+ has no reset jumper only a reset button.
I also tried double tapping the reset button, but this didn't change anything and COM-port is still not showing up.

Yes, I've tried the Bossa software, but that doesn't show the connection either.

I followed the points one by one.
When I connect the Duet to the PC via USB, only the two LEDs for 3.3V and 5V light up. The status LED remains off as well as all other LEDs.
I can't see a COM port in the device manager. Not even if I swap USB cables, USB ports or computers, even if I use a USB hub.
Also after performing the "Fall-back procedure #2" no COM port appears.

I bought my Duet 3D Mini 5+ Wifi from Rat Rig. When I raised my issues to them, they asked me to report this on this board.

After software update my Duet wouldn't connect to the SBC and status LED on the board stays off. I already tryed all recomendations hier in the board, using differnt USB cables, USB ports and computers but in no configuration COM-port is showing up in the devicelist.

Please let me know how to proceed.