The screen turns black (but not turned off) when I don't use a pen on it

The screen of my tablet gets black after a while if I don't use a pen on it. ( it never goes black while I use it as the main screen or a tablet). If the tablet works as an additional monitor and I don't put a cursor on it for a while it turns black, but once I hover it with the cursor or tap it with the pen it turns on again and keeps working for the next 10-15 minutes if I leave it be. Then it goes black again. My PC still sees the tablet all the time even when it gets dark. So the tablet is not switching off.  It feels like the tablet goes in some sort of a sleeping mode until I wake it up with any activity on the screen. I attach the video where you can see how it wakes up when I move a cursor on it.