The post links another that goes into the theory a little: https://shahriyarshahrabi.medium.com/in-the-valley-of-gods-s...

Apparently a combination of Mie and Rayleigh scattering.

- https://en.wikipedia.org/wiki/Mie_scattering

- https://en.wikipedia.org/wiki/Rayleigh_scattering

I think the effect the author is talking about is definitely caused by atmospheric scattering, but the painted effects are different. Those are more likely inspired by overexposure, aberration, HDR, etc. Makoto Shinkai specifically is a filmmaker and often emulates camera effects like lens flare.