How do I make the windows open fully when switching screens?

C

crystal

I have several files open, full screen. when I switch from one file to
another, the second file opens partially, looking like a split screen . . .
but split screen is not on. Each time I switch screens I have to click
restore to get a full view of the document. How did I get into that space --
and how do I get out?

thanks
 
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