@Misaka11037 胡說八道。這個 support 寫清楚了是 end-to-end 。https://support.apple.com/en-us/HT202303

Messages in iCloud
For Messages in iCloud, if you have iCloud Backup turned on, your backup includes a copy of the key protecting your messages. This ensures you can recover your messages if you lose access to your Keychain and your trusted devices. When you turn off iCloud Backup, a new key is generated on your device to protect future messages and isn't stored by Apple.

至於雲上貴州的問題，簡單點來說就是 NYTimes 爆了 Apple 已經把 private key 給了中國，中國區是可以解密 iCloud backup 的。解密之後那麼所有的信息都看得到了。也就是說非中國區的和中國區的聊天，通過中國區的解密可以看到全部。