From what I've read, it doesn't constitute a "back door" as you've alleged. Apple has the encryption/decryption keys for those mentioned services, but does not hand over said keys to authorities, and instead decrypt the data themselves and hand over the information to the asking party.

Also, none of this is new. Apple already clearly states what services are end-to-end encrypted and what services are only encrypted on-site. They'd have a web page that lists all of it for a number of years (iirc, ever since Appe Health debuted).