It’s worth making whatever kind of submission you can manage for this. The page even specifically notes: “Due to the short timeframe of this inquiry, the committee would appreciate submissions being limited to 1-2 pages.”
This bill will affect all users of social media in Australia, and may have a particularly negative effect on Fediverse platforms (like Lemmy and Mastodon) which are operated by individuals or small organisations that may not have the resources to implement age verification.
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 required age verification system (whatever that ends up being).