Correct. WhatsApp uses the Signal protocol, and there is zero evidence of them reading message contents except with the consent of one of the users involved (such as a user reporting a message for moderation purposes).
(And before anyone takes issue with that last qualifier, consent from at least one party is the bar for secure communications on any platform, Signal included. If you don't trust the person you are communicating with, no amount of encryption will protect you).
Discovering a backdoor in WhatsApp for Facebook/Meta to read messages would be a career-defining finding for a security researcher, so it's not like this is some topic nobody has ever thought to investigate.
Yet. Until they say "We delete these messages after X time and they are gone gone, and we're not reading them" Assume they are reading them, or will read them and the information just hasn't got out yet.
I mean we keep finding more and more cases where companies like FB and Google were reading messages years ago and it wasn't till now we found out.
They never had the plaintext of the messages in the first place, so they don't need to delete them. That's what end-to-end encrypted means.
In the former case, Facebook can decrypt the messages at will, and the e2ee only protects against hackers, not Facebook itself, nor against law enforcement, since if Facebook has the decryption key they can be legally compelled to hand it over (and probably would voluntarily, going by their history).