https://www.bobvila.com/articles/witch-windows/

It turns out that witch windows aren’t intended to benefit the broomstick-equipped crones of fairy tale lore, but are actually meant to thwart them. Witches don’t have the capacity to tilt their conveyances 45 degrees, so the tilted design keeps them from flying into the home. (Apparently, witches don’t even have enough brain capacity to recognize the many perfectly vertical windows through which they could enter, either.)