Closest option is watomatic but it only works with whatsapp and Facebook messenger. There are talks about expanding it to support other platforms

So the whole security and privacy claims are purely marketing.

Or just use Signal which already does this.

Not possible

However as you are in the EU, Facebook have to add 3rd party support to whatsapp. So that people on whatsapp can still message users who are not on whatsapp. Later in the future, group support will be added.

No time frame of when it goes live.

https://www.theverge.com/2024/2/6/24063705/whatsapp-interoperability-plans-eu-dma/

This has been my worry that some big tech company buys it out. There is latitude and longitude. But its not as easy to remember.