As you know iCloud run their services in different countries/regions.

I know nothing about other stuff on iCloud such as drive, but you should not use a iCloud email account from China region.

This is because, after my test, messages from iCloud China were just sent from a China server, which is in Guangdong Unicom.

 68.1.255.157.IN-ADDR.ARPA. 3600	IN	PTR	cu-gy11p00im-quki07202302.gy.silu.net.

Due to the strict internet censorship from China gov, your privacy is not guaranteed.

And you should read the related articles carefully when you use an account from iCloud China.

How Apple Gave Chinese Government Access to iCloud Data