Should I say
looking from the window
looking through the window
to describe the landscape that lies beyond the window?
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In my opinion, both would work but looking through the window makes the meaning very clear.
While from is used in this context by many, through really conveys the idea of looking through a medium, in this case the window's glass pane.
You can consider using looking outside the window as well. For instance,
"As I was looking outside the window, I saw a cat cross the street."
Results from Ngram for your reference-