I would attribute this to the difference between programming/coding, and software design or engineering. They’re related but different concepts. Just like a builder and an architect do different things and complement each other to get a building built, these are also two distinct steps. I do think it’s easier and more common for one person to (be able to) do both tasks than in my analogy though, but it’s also done separately often enough (in industry).
My point being: don’t beat yourself up that you don’t know programming, you probably do, it’s the software design that you’re not familiar with yet. But now that you know what is missing, you can look into it and work on it, and gain a valuable skill to complement your existing skill.
Thanks for the tip about SimpleX, that looks interesting! I could never use Signal due to the way they operate and force you to rely on their and Google’s servers, actively blocking forks from their network. So much for FOSS…