it has been a rockier history than that - it was playable at E3 in 2019, and there have been multiple teased (but not specific) release dates along the way. e.g. the Wikipedia has some of it: https://en.wikipedia.org/wiki/Hollow_Knight:_Silksong

to be clear: I'm not complaining at all, I'd much rather have a good very-delayed sequel than a bad one. but the "it's releasing again" -> "it's delayed again" memes do have reasonable origins.