DIAGNOSIS OnScreen Control requires a bidirectional USB connection for detection and control, not just the video signal from DisplayPort or HDMI. You have only a video cable connected.
FIX Connect the included USB upstream cable. Locate the square USB-B port on the monitor. Connect the USB-B end of the cable there. Connect the standard USB-A end to an available port on your computer. The monitor now functions as a USB hub. Install the latest OnScreen Control software from the LG website. Launch the software. It should now detect the monitor.
IF THAT DIDN'T WORK The specific USB port on your PC may not provide sufficient power or data. Try a different USB port, preferably a USB 3.0 (blue) port on the motherboard's rear I/O. Uninstall the OnScreen Control software. Reboot. Reinstall the software as administrator. Ensure no other monitor control software (e.g., DisplayFusion) is interfering.
HEADS UP The USB upstream connection is mandatory for features like screen partitioning (PBP/PIP), precise color calibration uploads, and firmware updates via the software. The monitor's USB downstream ports will only be active when the upstream cable is connected.