The Signal Foundation does work on Signal Desktop - but they only release binaries for Mac, Windows, and Debian-based Linux distros. Those are the downloads available on their website, there is no link to the Flatpak on their website.
The community turns that official Debian release into an unofficial Flatpak release. This means that you need to trust the community packagers to be doing the right thing, along with trusting the Signal Foundation. It’s an additional layer of trust that you wouldn’t need for an official release.
An alternative option would be building the app yourself - there’s documentation here and the repo is here, but then you’re responsible for keeping up and rebuilding when they have updates. I definitely hope the Signal Foundation releases an official Flatpak, it’s not a great position to be in if you’re not on a Debian-based distro.
You may like this pattern of starting all custom commands with a comma - benefits against a wrapper command would be shorter command names and built-in tab completion.