There are ways to implement age verification that address privacy concerns, for sure. It remains to be seen whether the government chooses to use them, or if they will use this as an excuse to de-anonymise Australian social media users.

In any case, blind signatures (or other cryptographic methods) won’t address the issue that Australians will be banned from any social media platform by default, until the developers get around to implementing the age verification system required (whatever that ends up being).