I'm sure the Chinese government is working on hacking iMessage if they haven't already. Likely the only reason they allow it is because (I'm guessing) many of the elite families use iPhones there for personal comms. But trust me, the CCP are working on it if they haven't done it yet.Which is able to be disabled. And iMessage still works E2E encrypted.
So they can just use signal you say. Well... https://www.nbcnews.com/tech/tech-news/encrypted-messaging-app-signal-blocked-china-rcna432
Ok. How about whatsapp: https://cybernews.com/how-to-use-vpn/unblock-whatsapp-in-china/
Maybe Telegram? https://www.scmp.com/tech/policy/ar...snares-encrypted-messaging-app-signal-joining
So, if you want E2E encrypted instant messaging.... what are you going to do? That is still legal in China?