But it isn't a privacy feature. A privacy feature would be to create an account with a password without mail validation.
I you use Apple ID, Apple gets the info which services you are using. The service might request additional infos about your person. Most people will always confirm that in reality. This way many services will end up with more user information. Many people will just share everything but might think about it if they needed to provide this info manually.
It is maybe a privacy feature because Apple might be better than Google or Facebook. Well...
Privacy , like security , has its own “threat models” and compromises depending on who you’re trying to get privacy from. So this is absolutely a privacy feature and it astonishes me that amount of people who don’t get this and try a No True Scotsman.
My mail provider would need to parse my mails to get info about what services I use. Identity providers have those apps registered and grand token for specific services. They know exactly when a user is logging to specific services. This data doesn't even need to be evaluated further, Apple would have a neat list about the services you use.
Still, the usual mail registration offers more flexibility and gives the user more control. So, email registration is a privacy feature if you argue like this.
Security wise it is a decent solution, but also a single point of failure. It is hard to argue this to be a privacy feature. It is only one if you trust Apple more than the other services and different forms of auth isn't possible.
I you use Apple ID, Apple gets the info which services you are using. The service might request additional infos about your person. Most people will always confirm that in reality. This way many services will end up with more user information. Many people will just share everything but might think about it if they needed to provide this info manually.
It is maybe a privacy feature because Apple might be better than Google or Facebook. Well...