As far as I know, their biggest problem isn’t reading chats (if device seized and unlocked, not a problem at all regardless of service and encryption level), but listening encrypted calls. This one really bothers them and WhatsApp appears to be threat number one. I don’t know anything about the scale of CSAM distribution there, but I think they don’t need ChatControl-like technology for dealing with it. ChatControl was worse than Russian surveillance state, maybe on par with Chinese tech.