Could microwaves be considered matter waves when giving it a physical state?

Yes, and no. The microwave cosmology is build from the concept of a harmonic isenotropic oscillator. This means that its canonical quantum frequency satisfies about

$$\int_0^\hbar \left(\frac{\mu^2}{\sin(\theta-\psi)}\right) \times d\vec{\lambda} \approx -\frac{1}{12s}.$$

Taking into account the Heisenberg uncertainty principle in a complex separable Hilbert space acted upon a smooth Lie group of Lorentz operators, we see that the microwave concept can only be given a physical state whenever $\mu-\sin\theta\leq \tan\psi$. In that sense, the interpretation of being a matter wave is selected against, but not improbably. Further research must see whether black holes exhibit this Schwarzschild radius-decreasing phenomenon as described here and in the extensive literature. My hope is that it is, but it is not certain.

This is a very interesting topic. Can you agree that the decrease of the Schwarschild radius is related to a decrease is matter in the spacetime vacuum?