Well they aren't supposed to be. But it's almost impossible to enforce.
From memory it's about 14 different platforms, far from definitive but catching the main sites. Facebook and Twitter have claimed that they have got rid of something like 6M accounts, but I think the figure is bullshit. There has been a few reports of people's accounts being frozen, but I reckon most of the accounts were probably dormant accounts.
It's easy to get around and plenty of kids worked out ways even before the rule came in. But of course it also took just as little time for the nefarious pricks to write dodgy work arounds containing spyware and other shit kids don't always see.
The platforms supposedly can be fined for non compliance, although I doubt they'd ever pay. There is also no criminality on the kids if they are using it, so basically it's a law that cost a lot of money and achieves sweet fuck all until the government wants to brag about it.
The biggest problem is that the age verification software is not very accurate and can be beaten quite easily. But it can also get it wildly wrong so it's far from the success the government is trying to make it.
Blanket bans because a government says so are never a good thing.