Do you mean that HN censors topics/comments which it detects based on advanced filters which search for meaning even when people self-censor and use language to avoid simplistic filters like regex?

HN also has a flagging system and some people really, really hate some kind of speech. Usually they get more offended the more visible it is. A single "bad" word - very offensive to them. A phrase which implies someone is of lesser intelligence or acting in bad faith - sometimes gets a pass, sometimes gets reported. But covert actions like lying, using fallacies to argue or systematic downvoting seem to almost never get punished.

Can you give examples?

The closest I've seen is autodetection of certain topics related to death and suicide and subsequently promoting some kind of "help" hotline. A friend also said google allows an interview with a pedophile on youtube but penalizes it in search results so much that it's (almost?) impossible to find even when using the exact name.

But of course, if a topic is shadowbanned, it's hard to find out about it in the first place - by design.