When birds fly into windows because they can’t see the windows, we often stick bird-shaped stickers on the windows to help them see the windows.
At the beginning of the summer, our family often walk into the screen doors because it has been so long since we used the screen doors.
So I attached a magnet shape to the screen door with a magnet on the other side.
My very funny wife noticed that I chose a human shaped magnet to attach to our screen door (kinda like attaching bird-shaped stickers to windows).
You can, of course, attach better magnets than the ones that I quickly chose for more secure attachment. And there is, of course, no guarantee that people will stop walking into your screen doors with this in place.