"You have to essentially pre-deplatform yourself."

For young people, "the only things that have the level of scarcity and danger required to be seen as cool" are "whatever is unacceptable on those platforms." In other words, anything (and maybe only things) that're blocked or banned are a candidate to be cool. Cool people walk away from the places where you'd expect to find them and hang out in places that are culturally viewed as less important.