According to this article, they way they bypass WhatsApp's end-to-end encryption is by gaining access to the host device itself, and then recording everything that's on the screen.

So this would mean switching to something like Signal (which is in principle more secure) shouldn't help.

I'm quite skeptical that they can do this in a general case - Perhaps exploiting some zero days on some Android/iOS versions? I don't expect Google and Apple to sit around and let this happen for too long though.