Can the usb-c Port of RasPi 4 used for anything else but Power ?
YES! The USB-C port can be used as a USB On-The-Go (OTG) port, both power and data is populated in the connector, see schematic.
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.