In the absolute nirguna brahman point of vew, pure awareness is not aware of itself. For it’s not an it—just the pure subjective self.
Yet being omniscient, parabrahman is of course self-aware. This is the saguna brahman point of view.
Because nirguna brahman is immutable, saguna brahman can’t be real. It’s reflexive universe is an illusion. But its realization isn’t.
Thus nirguna brahman and saguna brahman share a common brahman. It’s called self-awareness.