There was an article I read here posted by adywan (I can’t remember where though) where Spielberg recalled a conversation he had with George Lucas in a park back around 1981 where George told him about Obi-Wan cutting of Anakin’s limbs in a fight by a volcano, Luke’s mother lived afterwards, and how anybody could learn about the force.
There were a few more details to it but I can’t seem to find the article here.