For age verification and identity verification both afaik. Sometimes I wonder if what's needed is "just" a more public push for it, but these topics are so hopelessly technical, I think it has no hope to ever reach the mainstream and poll well. And that is ignoring all the other counterarguments against these that compound on top, some of which are culturally sensitive for many.
These topics are political and I seriously doubt these types of solutions are what the politicians are looking for. In fact, they are the exact opposite of what they are looking for because it takes away the excuses they are using and would lay bare what they are actually trying to do. BTW, I'm not suicidal and I bet you aren't either.
I saw a presentation about this 6 months ago, it looked promising for age verification for example, it's even an already done system, not a research article.
https://github.com/microsoft/crescent-credentials
But of course the thing would need users in order to attract users.