I don't know, but arguably the OS version is better for privacy, as each app can just trust the signal sent by the OS instead of collecting a bunch of personal/biometric data.
until they decide that the OS now needs to collect a bunch of personal/biometric data to avoid people lying about their age or tricking the OS into sending a different signal than the OS should.
> until they decide that the OS now needs to collect...
It doesn't. The device (not the "OS") is registered with government authorities. The device is associated with a single human for the purposes of age verification. And it's a one time action at the time of association.