Hi, the only way to get the webcam working connected to the monitor, is to have the USB-C upstream cable connected to the desktop/notebook, on which you intend to use the webcam.
If I connect a webcam to my S2722DC via the USB-A port, the webcam doesn't work. The same thing happens if I connect a notebook to the USB-C port, i.e. it doesn't get power. The S2722DC is connected to a desktop via an HDMI cable. Thank you.
S2722DC, USB-A webcam not working