Chinese iCloud is hosted in domestic servers[0] with custom HSMs (Hardware Security Modules) installed[1] to geolocate E2EE keys for Chinese users in Chinese servers.
If Chinese authorities demanded physical access to the data there is nothing Apple can do to stop them. There is no proof that Apple provides credible security to these users and no historical audits that suggest they can.
So when Microsoft responds to an American warrant (or NSL) requiring a copy of a customer's data stored on Microsoft servers, that is a "backdoor in Windows"?
Well, first off, I never called it a backdoor. I just laid out the pitiful security situation Apple created for their Chinese users. You're the one putting words in my mouth.
Secondly, yes, especially if it's OneDrive. Both iCloud and OneDrive are first-party software products, they are built-into their respective operating systems as native features. If BitLocker was compromised, it would be a "Windows backdoor" too.
If Chinese authorities demanded physical access to the data there is nothing Apple can do to stop them. There is no proof that Apple provides credible security to these users and no historical audits that suggest they can.
[0] https://support.apple.com/en-us/111754
[1] https://www.nytimes.com/2017/07/12/business/apple-china-data...