Especially seeing as WhatsApp’s former head of security blew the whistle recently, claiming that about 1,500 WhatsApp engineers had unrestricted access to the sensitive personal information of users.
In summary, there is probably no “real” backdoor allowing Whatsapp employees to read your messages. But unencrypted cloud backups (to Apple and Google) are enabled by default encouraged and most users won’t change these settings to enable E2EE for cloud backups - meaning law enforcement can request chat data from Apple/Google. Also, if a user reports a message to Whatsapp, that message and a few adjacent messages will be forwarded to Meta (which in my opinion is not a breach of E2EE per se, just how taking a screenshot isn’t).
I just installed WhatsApp and the backups weren’t enabled by default. Not sure if this is the case on Android. Ideally though there shouldn’t be any unencrypted backups, but then the government could sue iMessage for the same thing.
I think you are technically correct (the best kind of correct). It doesn’t auto-enable backups, but at least in my experience it keeps nudging you a few times to enable it and you need to click on “never” back up if you don’t want it.