The chain rule was explored by Gottfried Wilhelm Leibniz and Isaac Newton in the 17th century. Either of them would have ”invented” backpropagation in an instant. It’s obvious.
Neither are really inventions, they are discoveries, if anything the chain rule leans slightly more to invention than backdrop.
I understand the need for attribution as a means to track the means and validity of discovery, but I intensely dislike it when people act like it is a deed of ownership of an idea.