Kobra 3 mainboard with missing SW2

So down is GND, up is 5V in the picture

The opposite of yours, but maybe that's it for the K3M

Do you have labels on the back?

Anyway I guess there are some diodes to block reverse current..

This is my setup, the USB-C cable is already plugged to my laptop

dmesg -w on the left and lsusb on the right

If I just plug the board without SW2, the LED goes red and after a few seconds I hear 2 beeps (cause it boots)

Nothing on the laptop

Okay, then I use a USB drive (why not..) to short SW2

While I plug the USB JST connector

This time it did not work, so I guess I plugged the USB-C in reverse

Ok that was it, USB in reverse, so I reversed the USB-C connector

Now the laptop displays errors in dmesg

As soon as the cable was connected, maybe 1s after connection

Okay finally got it, after a couple of retries / reversing cable / changing cable

You see 3 lines on the left with New USB found

And the Fuzhou Rockchip on the right