I have look in this forum and on Google and there are people out there have the problem that Cubase 9 pro hold the screen active for ever, and no solution has published.
I have the same problem on all my 3 PC-computers (labtops).
Me too, seems like a feature. But I would like to disable it too…
Just a thought…
Maybe this is caused by having the option “Activate Steinberg Audio Power Scheme” clicked on? That option is found in the Studio>Studio Setup>VST Audio System menu.
I do not use the Steinberg power scheme. I use the computer “High Performance” power setting. Besides, I have never found out exactly what power setting(s) change using the Steinberg Power Scheme. I’ll never use it unless I see the details of what it specifically does to the computer settings.
Regards 
I have not have activate the Steinberg Audio Power Scheme" otion.
One thing I dont undrstand - Why we have this problem, I meen if many cubase users have this problem it will discuss more.
I found very little on this subject. That strange!
(That option is found in the Studio>Studio Setup>VST Audio System menu)