I'm guessing that what you are calling scientific 'knowledge', I would call [unproven] scientific theories based upon a [false] premise of naturalism/physicalism. Then the existentialist's point would be validated. But you still have to prove the science. As you have explained so coherently in a recent article, if I've understood you correctly, the Hard Problem cannot be explained philosophically. Neuroscientists still persist in trying to solve the problem, however, because they are addicted to the physicalist philosophy.

You ask how I support supernaturalism. In brief, it is the only credible solution to the Hard Problem. I've written at length on Medium about what I believe, probably much more than you would want to read. You would probably call it a New Thought melange. It's a mixture of the Perennial Philosophy, thus ancient religions, Christianity as it was originally intended, not the exoteric version that has come down to us, new-paradigm science, and Transpersonal Psychology, thus the ideas of my two modern intellectual heroes, Carl Jung and Stanislav Grof.

Your Gnostic point is correct, but only superficially? The experience may feel the same. But philosophically speaking, I'm not aware of any Existentialist who describes consciousness as spirit/soul trapped in matter. [I'm not familiar with the writings of Kierkegaard, who I believe was a Christian. Perhaps he said something along those lines?]