> The app automatically matches phone numbers with the user names in the group. Chinese authorities then only need to request the owners of the phone numbers from the local telecom service in order to learn the users’ true identities.

This is a flaw common to services that rely on phone numbers as IDs. In many countries, one cannot purchase a SIM card without showing ID (and the seller makes a photocopy of the ID to provide to the authorities). That means that there cannot be true anonymity. Know the phone number, know the person.

I am always baffled when people claim that PGP-encrypted e-mail is passé because it leaks metadata, when Signal and Telegram leak metadata too and, furthermore, metadata that can be immediately associated with a specific person in many countries.