The sinister turn at the end of the video points to the overall failure of Descartes’ philosophical method. While you can systematically doubt everything until you realize you can’t doubt that you’re the one doubting, making yourself the foundation of certainty ultimately leads to an inability to know anything about the world outside your own sense perceptions (as Locke and then Hume pointed out).
Descartes took us on an epistemological turn in modern philosophy, but unfortunately, it’s a dead end street.