They're using a Facebook product. The privacy damage already occurred.
* Unless you want to go into a conspiracy theory that all the Meta employees can see the source code and nobody has ever felt like whistleblowing about the backdoor Meta put into WhatsApp, that is.
Its still preferable to use Signal since now it actually supports numberless registration. Hopefully they will actually fee payable not via credit card at some point.
It's preferable to use Signal because they don't collect as much metadata as WhatsApp, and the client is open source.
I don't care so much about the numberless registration. Actually I don't even understand why people care so much about it.
Don't forget that metadata is not encrypted, so Meta know who you are writing to, who writes to you, who your contacts are, all the usage pattens of the app, and more metadata (not sure if it's still the case, but a few years ago WhatsApp even uploaded the battery state of your phone to Meta).