Geocities was the place to create and visit homepages for a large percentage of people using the internet in the 90s. You can see its influence in games such as Hypnospace Outlaw and modern hosts like Neocities.

Hypnospace outlaw and neocities, both even less known lol

What are the most popular games on Steam that focus on interacting with a 4chan-like website?

There are none because people can just go on 4chan and post.

Until now. But I hope they are able to get back up and running.