This is effectively the EU age verification system.

Your government (which already has all your details) generates certificates and you just give those out. The other side can the use simple public/private key verification to ensure the cert is valid. Also government does not get information who you gave the cert to and if you create a bunch and single use them the other side can’t follow you between uses using the certs.

The EU age verification system requires tying yourself to Google/Apple [0] (ie will not work with GrapheneOS) which is a non-starter. This means you will need a mandatory Google/Apple account. What if your Google account gets banned?

[0] https://github.com/eu-digital-identity-wallet/av-doc-technic...