I think one longtime HN user (Karrot_Kream I think) pinpointed the change in HN discourse to sometime in mid 2022 to early 2023 when the rate of new users spiked to 40k per month and remained at that elevated rate.

From personal experience, I've also noticed that some of the most toxic discourse and responses I've received on this platform are overwhelmingly from post-2022 users.