>absorbent or light diffusing material should be mandatory
Absorbency is bad because it causes overheating and IR astronomy pollution. Diffusion is bad because it reflects light toward Earth.
Specular surfaces (mirrors) can reflect light entirely into space and away from observers on the ground.
This explains why SpaceX created their own radio-transparent, space-rated mirror. They are offering it—at cost—for use by other satellite manufacturers.
https://www.teslarati.com/spacex-shares-how-its-making-starl...
https://planet4589.org/astro/starsim/2022-05-07_SpaceX_Susta...