DIAGNOSIS The EW3270U does NOT have USB-C video input. It has a USB-C port for service only.
FIX You must use a physical video cable. Connect your MacBook to the monitor's HDMI or DisplayPort input using the correct adapter for your Mac (USB-C to HDMI or USB-C to DisplayPort).
IF THAT DIDN'T WORK Ensure you're using the correct source input. Press the monitor's 'Source' button. Select 'HDMI' or 'DisplayPort'. The USB-C port will never show as a source.
HEADS UP Many users confuse the USB-C port for video. It is not. Read the port labels on the back. Use HDMI 1, HDMI 2, or DisplayPort.