I get your point. And yet, the existentialist philosophers were at loggerheads with Kant over his over-use of reason. One major difference between them is their view on the important of “reason”. For existentialists, irrational is an inescapable attribute of human nature. And somewhere this is what helps us in negotiating with the absurdity of the world.
But again, Kant’s Categorical imperative seems to well utilized in the case of negotiating with absolute freedom. We are absolutely free to do anything. But, as you so well explained in this article, we cannot do “anything”.
That was something new for me to learn.