I check this WIP update.The Game window will now change properly depending on the camera and FOV.
BTW.
Could you create a inspector window with cameras in the scene? This would facilitate a quick switch between them.
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I found problem. Main camera don't refresh when we change active camera.
In this case, it helps to manually change the "projection" option to Orthogaphic and change again to Perspective in Main camera options. See image below.
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