Loss of full screen preview

How come full preview mode no longer works? I'm trying to blow up the main screen, leave it standing put a camera in front of it and just stream "commando style" (because my cellular bandwidth is way better than my home bandwidth and there are restrictions on cell phones which prevent them from being home bandwidth). I select the monitor the only monitor that the computer sees and it doesn't blow up the entire screen to be the whole picture.

No I understand the problem that if you want to edit you can't edit and simultaneously show the whole picture without getting up the controls.

Before I was able to get a full screen and shoot commando and if I ever wanted to edit I just pressed the scape on my keyboard and it brought me back to the edit screen as opposed to just the full screen picture.

Now that full screen preview has been neutered how do I get a full screen on my TV of what I want captured on Twitch when I'm filming commando? I have a very special effect i'd like to do, like red and cyan anaglyphs
 
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