Please follow below steps to turn on the Win10 Stream HDR video function:
(1) Use another Win10 PC/NB and graphics card that supports the HDR function and then connect to the monitor for the crosscheck.
(2) Go to Win10 System -> Display -> Turn "ON" HDR setting in Win10 HDR WCG.
(3) Open the Settings App and Navigate to Settings -> Apps -> Video Playback -> Turn "ON" Stream HDR Video function.
If the issue still exists after the steps have been performed, please contact BenQ local service center.