USB Input

My computer is connected to my console by usb (in USB-B mode).
I do not understand why the signal arrives on the console in 1 and 2 and sometimes in USB (input after ST3).
In the I / O menu this USB input does not appear.
Thank you for your help

@jb07

In the I / O menu this USB input does not appear.

Which i/o menu? Mixer or DAW?