How does the Rng for Pokemon battles work?

Question

I know Pokemon battles use a Rng code to determine whether moves hit or not and secondary effects. I want to know the following 2 things about the Rng codes.

1. I want to know when and how the code is determined,
2. if I can figure out what the rng code is by observing whether moves hit or not or if their secondary effects happen

Also answers for any of the gen 8/9 games are fine though I would prefer an answer that covers Pokemon champions.

Comments

I'm pretty sure in a recent gen they introduced a better RNG system that didn't just run a function on the time of day, so I'm not sure studying when moves hit and don't will let you abuse it

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Not for sure if this is a full answer, but Showdown used to use Gen 5’s RNG system: https://www.smogon.com/forums/threads/on-rng.3758023/
https://en.wikipedia.org/wiki/Linear_congruential_generator

This post also suggests that the rng system for some gens are either unknown or the findings kept private for the sake of the competitive aspects of those games.

Someone made an interesting post on Smogon about how they reverse engineered the RNG on Showdown if you want to read about it: https://www.smogon.com/forums/threads/rng-manipulation-in-pokemon-showdown.3757177/

(Btw Showdown changed the entire way they generate RNG seeds because of this)

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Huh thats cool. I’m still interested about champions rng because I've lost a few too many games to double heat wave misses or 10 percent free chances to not want to how the Rng works.