4chan is probably one of the least brain damaging sites kids can go to these days. It has porn and stupid memes, true. But so does google if you turn the safe search off. It's the corporate run sites and services with ai powered recommendation engines that are the most problematic. Infinite scroll sites like reddit or tiktok are what really fucks up your brain. I used to frequent 4chan as a kid back in the day when it was truly a wild corner of the internet and I turned out just fine.
Low quality porn at that. Their size limits and board post limits keep it that way. Only /gif/ and one other board even permit sound. That is hateful against the visually impaired.