DIAGNOSIS Bandwidth overload on the HDMI connection. The monitor is 4K 60Hz. Your source or cable can't handle the data.
FIX First, disable HDR in your source (PC/console) settings. If flickering stops, it's bandwidth. Get a certified Premium High Speed HDMI cable. Ensure it's connected to the HDMI 2.0 port on the monitor (port 1).
IF THAT DIDN'T WORK The flicker could be from the monitor's Brightness Stabilizer feature. Press the menu button. Go to Picture > Brightness Stabilizer. Turn it OFF. Test again.
HEADS UP Using DisplayPort can be more stable for 4K 60Hz HDR. Requires a DisplayPort 1.2 or later cable.