Is it really unused? The RPi4 schematic is incomplete, but it at least shows the USB 2.0 pins of the USB-C port going somewhere; they might be going directly to

Is it really unused? The RPi4 schematic is incomplete, but it at least shows the USB 2.0 pins of the USB-C port going somewhere; they might be going directly to that built-in USB controller in the main SoC.