**The USB-C "Power In" port doubles as a USB-OTG port** (or dual-role port (DRP) in USB-C speak).

[Overview for the Pi 4](https://www.raspberrypi.org/documentation/hardware/raspberrypi/usb/README.md):

> The OTG hardware present on previous models of Pi is still available and it has moved to a single connection on the USB-C port. The OTG hardware is intended to be used in device-only mode on Pi 4.

<hr>

The USB-C port is the only connector left that could provide USB OTG connectivity, even though the [spec](https://www.raspberrypi.org/products/raspberry-pi-4-model-b/specifications/) does not list the OTG port explicitely.

The [official schematics](https://www.raspberrypi.org/documentation/hardware/raspberrypi/schematics/rpi_SCH_4b_4p0_reduced.pdf), top left, show the USB-C Power In connector which is labelled "USB2 ONLY" and has the UUSB_D_N and UUSB_D_P data lines connected, pins A6, A7 and B6, B7, which are relevant for USB 2 (and OTG).


[![enter image description here][1]][1]

<hr>


[Transition Existing Products from USB 2.0 OTG to USB Type-C](https://www.ti.com/lit/wp/slly017/slly017.pdf) tells:

> In the Type-C ecosystem, the USB 2.0 OTG device 
is referred as a dual-role port (DRP). A DRP is a 
device that can function either as a USB host or 
as a USB peripheral. In Type-C terminology, a USB 
host is called a downstream-facing port (DFP), and 
a USB peripheral is called an upstream-facing port 
(UFP).


  [1]: https://i.sstatic.net/LDSst.png