No, I don’t think we can, or need to, invoke some third thing — an observer — to give reality to mind or matter. The lack of inherent existence of mind and matter refers to the idea that existence is not something that inheres in any particular entity, whether a mind or a physical thing. All existence and all properties are derived from the whole. So mind and matter do exist, but they exist relationally and relatively. I like the metaphor of a rainbow here. It appears like a bridge that exists independently of the observer at a certain place in the sky, but this independent existence is an illusion. It is a relationship between the observer and the sun as a light source and refracting water droplets in the atmosphere.