How is it possible, that Signal still only provides a .deb package and no .rpm, or even better AppImage or Flatpak? There is an unofficial Flatpak but is it secure?
Just because something is built out of love does not make it safe, and attestation is about safety. You wouldn't trust an un-attested surgical device, just because there's a really positive community around its design.
I just read through the unofficial Flathub Flatpak for Signal and it is very simple. It fetches the .deb from Signal's website, installs it in the sandbox, and uses a launcher script to tell the OS some basic toggles like should it start minimized or should it display a tray icon. In the script it makes use of zypak, which to my understanding is to tell electron (chromium) to allow sandboxing to be handled by Flatpak. Here is the repo and the build instructions is the .yaml file.
Flatpaks are pretty easy to read through. Just go to the links section of Flathub and click the manifest, then read it to see what is done during building.
I mean it’s FOSS. Have you considered opening a PR to contribute what’s missing? You can be the change you want to see. I wouldn’t normally comment something like this. Your emphasis on “still” raised my hackles a little bit and led me to ask why you still haven’t made your own.
All of these packaging systems have plenty of tutorials. Speaking from experience, many maintainers were not developers when they started maintaining packages for distros other than the official distros. I have worked with several maintainers who do work in tech and know socially several who had no background. This could be a great place for you to start!
You bother because FOSS is as much paying it forward as it is getting shit for free.
Some projects of Signal-compatible clients and forks received a message from a Signal representrive requesting they stop distributing unofficial clients that connect to their servers.
That probably has on shilling effect on Linux distribution that may be considering building and distributing Signal in their repository.
They can't possibly provide a package for every distro.
Signal's model, ie keep tight control over development and distribution of the client, and the absence of federation, it well suited for Apple/Google's stores, but not at all for open-source and Linux' ecosystem.
Could always do what looks like the Arch AUR package is doing and build it yourself from source. Or if you are running a Fedora/OpenSuse distro you could find a package on COPR or something that converts a package from a .deb to .rpm and just change source and stuff to match signal.
Building from source is the opposite of hacky. It's the recommended way to deal with things like this where you are concerned about trust and security. I understand that it's not something you've done before, but it not as complicated as it sounds. There are many tutorials on how to build programs from source.
I understand that providing official packages for fedora/rhel, Ubuntu/debian, and arch-based distro packages along with a flatpack and Appimage would make a lot of sense, but for whatever reason, signal has decided not to. Perhaps you can message the signal team to ask why they choose not to do this.
It's an old program that converts between .deb (Debian), .rpm (RedHat), .tgz (Slackware), .slp (Stampede), .pkg (Solaris), and LSB packages.
I don't use it much, but it can be handy in a pinch for installing software that isn't packaged for your distribution. Just don't use it for anything low-level or that's already packaged natively, or you'll break stuff.
OP, what distro are you running? You mention a whole bunch of package formats they don't provide, but never mention what format you require. Depending on the distro, making a build script (or converting the .deb) really isn't Rocket Surgery ™.
What percentage of Signal users is "grandma" that uses Linux and would be messaging from her PC? I would have to imagine the overwhelming vast majority of Signal users are on mobile only, so packaging for specific distros is probably far down the priority list.