Is Kant's "proof" still valid?

"Mathematics, Philosophy, and the Real World" seems to say that Kant's "proof" is no longer valid.



Lecture 27 Describes

Kant's classification scheme, which confines metaphysical statements such as "every effect has a cause" to a category called a priori synthetic.

Kant's "proof" cites Euclid's "parallel hypothesis" which which physicists no longer believe holds "in the Real World".