This law doesn't actually change that, necessarily. It applies to "social media", and not to "chat" applications. As such, Discord is apparently not included (though I'd argue it really should be, under the letter of the law, because it straddles the line between chat and social, but in my experience it sits mostly on the social side of the line), and apps like What's App, Messenger, and Signal are definitely exempt. The law also doesn't actually require deanonymisation. Just reasonable steps to demonstrate they are old enough.

You can see how AZ has chosen to go about complying. Other sites might comply just by looking at the age of an account, or usage patterns (e.g., accounts that have talked about jobs, taxes, and home ownership might be presumed to be older, while accounts that talk about Roblox are assumed under age). Or they might use the identifying options of facial recognition and government ID, but through an intermediary so the site itself never traces your account to your real ID. Indeed, this last option is arguably how it should have been required to be done—using blind signatures or zero-knowledge proofs involving trusted age verifiers—with methods that could identify the person directly being banned.