“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)

https://techcrunch.com/2024/03/04/signals-meredith-whittaker-scorns-anti-encryption-efforts-as-parochial-magical-thinking/

So no interoperability in the near future for Signal.