There are a bunch of online spaces that are like this. Someone - Helen Joyce probably - was saying that there's an element of kids raising kids online and their parents not knowing what's happening.
For girls I think it's certain Tumblr or Reddit communities, since they've cracked down on the anorexia ones it's been trans and more recently spoonie communities.
For boys it seems to be porn, gaming or weird political subcultures, and with the political/cultural side it's a random throw of the dice whether they become wannabe fascists or wannabe communists or Andrew Tate followers or they pretend to convert to Greek Orthodoxy and start banging on about reconquering Constantinople. Any ideology will do if you can make it edgy enough.
This was one of the issues with Rudakabana, wasn't it, he'd been referred to Prevent multiple times but they couldn't deal with him because he didn't have a consistent ideology. In today's online world, trying to clamp down on specific ideologies starts to look like a very Tony Blair era analogue solution.