Threema is Swiss, which is a regional EFTA member. It's end-to-end encrypted and the clients are open-source.
Zulip has client-server encryption, which is fine if you control the server.
Zulip has client-server encryption, which is fine if you control the server.
https://comitiscapital.com/news/comitis-capital-announces-th...
Not sure what / if that changes anything, but presumably it will… sometime…