We've filed plenty of reports here at UT warning about the potential impact of Starlink and similar satellites on the field of astronomy. We've gone so far as to point out that the granddaddy of space-based telescopes—Hubble—has already had some of its images tarnished by passing Starlink satellites.
Yeah, as far as I know, they aren’t required in any way to try the sun shields and dark paint. It seems like they’re doing it out of a mix of good will and probably trying to avoid causing new regulations. It’ll be interesting to see if future Kuiper and OneWeb sats do the same.
SpaceX wants new regulations regarding satellite brightness.
Their own satellites (at least the second generation ones) fulfill the requirements set by the astronomers at the Rubin Observatory, +7 mag (10x darker than the original ones). Meanwhile the satellites of the competitors OneWeb and Amazon can’t fulfill them without major design changes, because the altitude the satellites orbit at makes a significant difference.
If the recommendations of the Rubin Observatory report were turned into regulations now, Starlink would barely be affected (they’d just have to stop the gen1 sat production a little early) while the competition would be set back several years.