DIAGNOSIS Windows Update replaced or removed the correct touchscreen driver for the monitor's specific chipset. The monitor is now being recognized as a generic PnP Monitor without touch functionality.
FIX You must manually install the touch driver. Go to the official KYY support website. Download the driver package specifically for your monitor model (e.g., KYY 15.6 Inch Portable Monitor Touch Driver). Run the installer. Restart your computer. The touch function should be restored.
IF THAT DIDN'T WORK The monitor may have switched to a non-touch video mode. Press the monitor's physical OSD menu button. Navigate to the 'System' or 'Other' settings. Ensure 'Touch' is set to 'On'.
HEADS UP The touch function requires both the correct driver and adequate power. If you are using a single USB-C cable for both video and touch, the power delivery may be insufficient. Use the two-cable method (one for power, one for video/data) for reliable touch operation.