As others have said, it’s obvious that no real attempts have been made by anyone to create a privacy-focused solution because the end goal is to collect photo IDs.

Occasionally in my free time I have been tinkering with a certificate-based solution that could fulfill this sort of need for age verification. It’s not the most robust idea but it’s simple enough using most of what we already have. Creating a minimal protocol which doesn’t share actual identifying information nor metadata of the site you’re accessing is trivial. If I can make an 80% solution in less than 100 hours of my free time then some groups with more money and intelligence could propose a dead-simple and easy-to-adopt solution just as easily.