Matrix should not be considered as their security has been pretty bad until recently (they intentionally shipped bad code and knew about it for years): soatok.blog/…/security-issues-in-matrixs-olm-libr…

Threema has been pretty bad historically: soatok.blog/…/threema-three-strikes-youre-out and their desktop pffering is not one-to-one with the mobile apps, it’s pretty limited in what it can do and has to have a device connected to the network at all times, open on the app and unlocked with the screen on.