“I think the spirit makes a lot of sense. But of course Signal can’t interoperate with another messaging platform, without them raising their privacy bar significantly,” even ones like WhatsApp that support end-to-end encryption and already partly utilize the protocol. “Because we don’t just encrypt the contents of messages using the Signal protocol. We encrypt metadata, we encrypt your profile name, your profile photo, who’s in your contact list, who you talk to, when you talk to them. That would need to be the level of privacy and security agreed across the board with anyone we interoperated with before we could consent to interoperate.”

-Meredith Whittaker (Signal President)

techcrunch.com/2024/03/04/sign…

So no interoperability in the near future for Signal.

Signal's Meredith Whittaker scorns anti-encryption efforts as 'parochial, magical thinking' | TechCrunch

AI is "not open in any sense," the battle over encryption is far from won, and Signal's principled (and uncompromising) approach may complicate

^{Devin Coldewey (TechCrunch)}

There's some confusion because of the reference to "Signal protocol". This refers to the key exchange and encryption protocol originally developed for Signal and adopted by WhatsApp, iMessage, and others.

This is a means of establishing a secure end-to-end encrypted conversation, not a federated protocol for different messaging networks to interoperate. WhatsApp announced that Signal protocol or a compatible E2EE implementation is one of their requirements to allow third parties to interoperate.

Signal has signaled its intent not to interoperate with WhatsApp or anything else several times over the years for both technical and security reasons.

...are there any unofficial WhatsApp clients I can use to preserve my privacy?

Using WhatsApp and 'preserve privacy' is a contradiction. Accept no privacy or stop using any kind of Metas services and networks