Shameless plug: I wrote about hash chains some time ago. They are a nice and simple solution to age verification. https://spredehagl.com/2025-07-14/
When some country parliament decides to mandate age verification, it's really easy and lazy for them to just say "verify ages and do it reliably!" and stop at that. As a result, the services affected don't really have a choice to go towards those horrible solutions of scaning our faces or IDs or both and all the issues around that.
What should happen rather is "we'll build a system for age verification that is privacy focused and all you sites that are adult only will have to use it or any other system we deem acceptable" But this requires effort on the part of the government doing the law. And money.
I know that the preparations for eIDAS 2.0 (the European thing) did contain many good parts. Taking inspiration from SSI. So at that point their specifications were rather good. I havent kept up with it for almost one year now, so that might have changed.