Not only that. If they want to intercept e2e chats it's possible with a MITM attack, that if you control the server it's not a difficult thing to do. Of course the users if they check the keys they see they are different, but practically no one does that.
And I think WhatsApp probably does it, otherwise why the authorities never complied that WhatsApp did not let them see the conversations?
WhatsApp has defaulted to aggressively storing allegedly "E2EE" conversations without any form of encryption in Google Drive (freely) for years. And it would seem they are also currently in possession of the keys to decrypt them when you restore such backups from another device without the key stored on it (that lately cannot be extracted without exploits or root access anyway). Facebook/Meta has often expressed their love for the practice of client-side scanning or parallelly sending data to their servers, but it doesn't seem the case for WhatsApp yet, so what measures they take to remain compliant with the ever-increasing surveillance practices remains to speculation. For a somewhat educated user that knows to opt-out of online backups every time it's prompted by the application, I'd say it's probably safer than normal Telegram chats, but very far from flawless.
And I think WhatsApp probably does it, otherwise why the authorities never complied that WhatsApp did not let them see the conversations?