WhatsApp uses the Signal Protocol. Is it as private as Signal? No, it "leaks" way more metadata. Have I personally checked if they're encrypting messages? Also no, although others have. Is it possible that they're doing something "funny" and no longer encrypt? Yes, but is there any suggestion or proof of that being the case?
Should you use WhatsApp? No, but the suggestion above was to use Telegram, a service that doesn't do end-to-end encryption by default and leaks the same type of data as WhatsApp. Going from Messenger to Telegram is a sideways move. From Messenger to WhatsApp would be at least a small upgrade (with the benefit of having more contacts there than Telegram, at least in some countries).
I understand the point about it also being a Meta app. I guess the question is what do you trust more? Telegram and the people behind it with your plain text messages or a Meta app with end-to-end encryption? I don't trust either, so I pick encryption.
I'm not anti Telegram or anything like that. It's a nice app, lots of features, smooth, etc, and I use it, but privacy was never their main priority.