Some feedback on the Guide pages, though I don't know how many new users actually read them, let alone discover this website in the first place:

It might not hurt to explain what the "DQN" board is on the intro page (https://4-ch.net/guide/view/introduction). Something like "The mysteriously titled 'DQN' is an anything-goes board for comedy threads and casual social chatter in the vein of the famous 2channel board News4VIP. Its name comes from 'dokyun', a 2channel meme meaning approximately 'dumbass.'"

When I click on "Joining in" on https://4-ch.net/guide/view/introduction within the main page frame, my browser (latest Firefox) throws the console error "Blocked loading mixed active content “http://4-ch.net/guide/view/participate”."

https://4-ch.net/guide/view/participate links to https://en.wikipedia.org/wiki/Sage_%28Internet%29 which doesn't exist.

https://4-ch.net/guide/view/history is kinda boring. It could mention that 4-ch was part of the iichan/wakachan network before it died, and possibly say something about the IAA board. (I'm not sure whether it was actually deliberate, but since IAA was never linked to from iichan, I got the impression it was originally a 'secret hangout' for elite 4-ch posters, which seems an interesting footnote at least.) Not sure any of the other removed boards are worth mentioning.

Also, possibly deliberate and not really a major issue, but Requests is linked twice on the sidebar, once at the top under General and once at the bottom.