Earlier quoted context omitted.
So you are going to move from one centralized, walled garden, privacy hostile platform that hard requires Google/Apple ecosystems to get signed updates... to another with identical drawbacks. I suggest something that lets you use any client/platform you want, uses the same crypto primitives, and lets you choose what server/country your data is hosted in and change your mind any time, e.g Matrix. How many times do cen…
Matrix is riddled with bugs. While I agree with you that signal isn't all that great (they do some really good stuff and then make some really weird trade-offs), I've recently compared Signal, Wire, Threema, Jami, Briar, Element/Matrix, and Keybase. The most mature app is Signal. It has the best usability to privacy trade-off. Threema is the better choice if you don't mind not having a usable desktop client. For me t…
Seeing as you mentioned Threema in the same post, I think I ought to step in here.
The encryption protocol for Threema is open source, using standard algorithms, not something they invented.
You, like I did for $my_org, can write your own software to send messages to devices running Threema using the Threema API.
Message contents are, of course, encrypted before submission to the API. Threema provide a number of SDKs to help you, but you are under no obligation to use it, you can write your own API submission client from scratch.
P.S. Not saying Wire is bad here. Wire is good. I use it alongside Threema myself for $other_uses. But I'm saying don't write off Threema under a false understanding that their encryption protocols are closed source.