This question already has an answer here:
In the GoT finale, Sansa said that Bran couldn't father a child. And then, this fact was used by Tyrion Lannister to persuade Grey Worm that
this is what the dead Daenerys meant by breaking the wheel.
My question is: How could anyone know that Bran was infertile? Nobody had access to advanced technology to determine that and Westeros would definitely have seen crippled people fathering child.