Some USB-C adapters offer a video output as well as a standard USB output. Such an adapter (for example with a USB port and a HDMI port) can handle simultaneous outputs: i can have video coming from the HDMI port while transfering data to a USB disk with the same adapter.
I am assuming the video output is coming from an USB alternate mode (HDMI in our example), so this means both signals go through the same pin. How does this work in practice?