The output from the bake is grey for the plane and flat white for the pyramid. When the image texture is used as a sculpt brush it doesn't create the same pyramid shape that was used for the bake. Don't know what I have done wrong could I have some help please.
I really don't think you can have such a deep point on a displacement texture. That's why it just bakes a white square. Your brush is essentially just a square brush.
I quickly made an example of how the texture should actually look like. It's not precise but it's to give you an idea.