Secret back-doors never remain secret, and they are often exploited by threat actors. just look at the recent issues with Chinese state actors utilizing the secret backdoors in the US telecoms networks.

https://archive.is/EzboV

If Apple is being asked to do this, then so will all other major cloud storage vendors.

Of major concern is that many authenicator apps store their data in a user's Onedrive/G-Drive/iCloud account (as do many password managers).
If these accounts are compromised by adversaries (including nation states, competitors, and general ne'er do wells) then the implications are significant.