We're the product of all the information we consume, but forums like HN aren't custom-tailoring what I'm shown to maximize engagement from me.

Do you think there might be some variation in the degree of negative effects a forum like Hacker News has compared to TikTok/YT shorts?

No, because reading is more healthy than mindlessly watching short videos. There is only so much content on the front page, it's not a slot machine you can pull for hours like tiktok.