As part of changing laws in Europe, Meta now offers the option for you to chat with others using third-party messaging apps that have integrated with WhatsApp and that you choose to turn on.
Note: Chats with third-party apps are only available in select regions and may not be available to you.
I feel sorry for all in the wrong region.
The only choice so far is Birdychat, which is business related. I’m afraid Signal would be hard to integrate due to its encrypted nature (and the fact that it’s not European). I hope Threema will follow.
Unfortuantely I only found this German heise news from Feb 2024. But both Signal and Threema won’t lower their security and privacy standards to be interoperable with WhatsApp.
I also have haiket allowed.
No FOSS options.