It’s technically impossible, so a pretty pointless discussion.

And it’s dangerous too. Even if they legislated them off the major platforms, there’s a million other ways to communicate online. Hundreds of DMs, talkers, games, live chats, streams, even IRC still exists. And pushing them into the darker corners makes it far more likely for them to be exposed to coercive and controlling types. Extremism, child abuse, bullying, suicide encouragement and so on.