The provided pictures don't really do a good job of showing when the notch is enabled, since it is showing the exact same thing - in both cases the top area is being used for status like battery etc. On the iPhone X a "notch aware" app can use that part of the display for itself (i.e. no status bar) and I assume that the newer version of Android that is supposed to be "notch aware" will allow the same.
If all the iPhone X could do is use the top area for status, then of course you'd want it black all the time! To get a proper comparison of notch on/off on the P20 it will have to be running that latest version of Android that fully supports the notch.