I would personally simply heavily tax ad revenue rather than banning social media, as while a blanket ban is ironically less of an infringement on free speech than banning it for children, it’s still something of an infringement.

There’s a bunch of benefits to an ad-tax too, beyond revenue generation: Users won’t be encouraged to use VPNs (and most VPN users probably also use ad blockers anyway). It’s difficult to evade, since an advertising business kind-of has to operate in the open; if nobody knows you’re running an ad business, your ad business has failed at the one thing it’s supposed to do. Advertisers are also purely profit-motivated, and so won’t hesitate to rat out their competitors if they’re using some loophole to gain a competitive advantage. It’s also very difficult for them to hide which country they’re targeting, since that information has to be available to their customers, so the taxmen can get it by subpoenaing customers or posing as them. And there’s not that many big ad-tech companies, so you don’t really mind if a few small-fries slip through the net.