It's true - the universe is made of nothing. Galaxies are mostly empty space. So then you find some matter in the galaxy. Atoms are matter. But atoms are mostly empty space as well. But then you find the nucleus. But protons are mostly empty space as well. But then you find quarks. But quarks are mostly empty space as well. It's empty space all the way down. Nothing actually exists.
On the other hand, we can detect atoms, nucleons, quarks, and even, in so called empty space, vacuum fluctuations. Maybe it's more accurate to say nothing doesn't actually exist.