Thanks but no thanks.
There ought to be better solutions.
My view is that it's a question of culture. In particular, the eradication of any sort of authority (parents, teachers) and the worshipping of "I want, therefore it's good and my right" are among the root causes for this epidemic.
Just something on top of my head, I'm sure that there are solutions to this. It's the political will and balls that are nowhere to be found...
Denmark have MitID, which is a sort of government OIDC/OAuth2 thing. There's no issue in having it expose only a single claim, such as age, or adult=true/false in age verification scope. You don't have to open the floodgates to government data, in fact Denmark has navigated that pretty well through the last three iterations of our government issues online ID scheme. There's even laws preventing cross referencing data from different database, in the case that you for some reason have access to it.
What about having IRL stores sell one-time use age verification tokens after showing ID? Just like tobacco or alcohol they can make it illegal to provide them to a minor. Whereas if you're worried about privacy you can still buy with cash.
The store sells a scratch card containing a single-use code, after you show them ID. When you sign up with whatever social network, you enter the code and the social network validates it with the code provider service. That's it.
At best the code provider can tell the social network which store the code was purchased in. Drive over to the next state to purchase codes if you're paranoid. Mandate by law that no records of code purchases or copies of ID are kept. We don't require it for alcohol or tobacco purchases so there's no justification here.
Sure, it adds more steps than just "click this checkbox if you're an adult" but kids/teens are a crafty bunch and, unlike drugs and sex, a) the penalty for violation of the rules is not immediately obvious (to the youth, OR even to society) and b) the act of violating the rules is not obvious in itself to people who aren't on that person's phone: there's no physical items left behind for parents to notice.
Effectively what we're talking about here is trying to solve the Sybil Problem, which has no widely-accepted solution.
There's no database of alcohol or tobacco buyers. The sales clerk just checks your id and forgets about it. It's a code good for use on exactly one account on one service, and expires in maybe a year. If you have multiple accounts on multiple services, buy separate codes for each one. They should be reasonably priced - no more than $5 each.
You don't need a perfect solution. Despite laws against underage drinking, smoking, and drug use it still happens.