I didn't mean "illusion" for something that doesn't exist. But to my understanding buddhism is a lot about that "what exists" creates illusions in our mind and understanding of who we are, how we are and what the world is. And to my understanding buddhist spirituality is a lot about getting rid of those illusions.
So for example in my practice this meant: Don't regard your body, don't regard pain or hunger. Sitting is not about regarding one's body and even not about regarding one's "self".
Sure. Nor is it about regarding anything else. Again, we have filters: Buddhism says "Don't regard your body", and Western thought inspired by Christian morality says, "Aha, Buddhism is about denial of the body and the body's desires!" But of course it isn't.