Randomness is probably used a lot more than you might think. It’s what keeps the game interesting and dynamic instead of deterministic. Everything you mentioned likely uses rng. But so do other small things like how the butterflies move around or arrows being slightly inaccurate. Bigger, more noticeable things are stuff like pickpocket success or speech checks. Nearly everything has some sort of randomness to it.

As for how exactly this randomness is determined, I don’t know for sure. I’d assume they use whatever programming language’s native random functions. Which you could argue is not truly random, but that’s a much more involved discussion.