About cloud rendering: In 2008 a college friend wrote his thesis on real-time realistic rendering of clouds: https://maverick.inria.fr/Publications/2008/BN08b/

You can see screenshots of that work in his thesis defense slides https://theses.hal.science/tel-00319974/file/defense.pdf

That's where I learned about the transference phase function (slide 24), which includes two spikes on the return angle that correspond to the relatively unknown Glory rainbow: https://en.wikipedia.org/wiki/Glory_(optical_phenomenon)

I don't know if this method is what is used in video games today.

Incidentally, you may recognize his advisor Fabrice Neyret as someone very active in the Shadertoy community https://www.shadertoy.com/user/FabriceNeyret2