A few years ago, for about a month it was obsessed with videos of red-hot knives cutting through things. It was ridiculous. To the point where "professional Youtubers" with no previous history of videos like that needed to ride that wave just to be relevant.
Think about it: some person in their house heating up a kitchen knife over the stove so they can cut through a bar of soap, simply because an algorithm decided that's what people on some video site want to see.
Then it was Family Guy clips, which is still happening.
And "relaxing low-fi music to study/relax to", which I'm pretty sure at least a billion people on planet Earth have seen recommended to them at some point.
I'm sure there are many other examples, those are the ones I remember.