Linux

Oh I'm very sorry, I didn't see the period before the At the expense of storage space

Flatpaks either work for everybody, or they don’t work at all.

Maybe? I've seen enough people having weird issues with flatpaks that others don't have. One recent example was somebody complaining here that the firefox flatpak took very long start, which I found odd because flatpaks aren't compressed squashfs images and should not be taking long to start up, that's an issue of appimages and snaps instead lol.

Packaging your software with Flatpak does not mean you won’t have issues. But when you do have issues, you know they’ll be an issue for everybody. So when you fix it, you also fix it for everybody.

Another issue that I've noticed with flatpaks is that they are usually built with generic flags, I don't know if this is a requirement or lazy developer, but this is also an issue that yuzu had, the flatpak was built for x86-64 while the appimage was for x86-64-v2 and that had a 8% boost on fps at the cost of people with cpus older than sandy bridge not being able to use it. (Which I mean if your cpu is that old you can't use yuzu anyway).

EDIT: And by weird distro I basically meant nix or musl distros, which I know flatpak works on because it bundles an entire distro basically, while appimage tries its best to be compatible with every distro provided it uses glibc and follows the FHS.

On that there is no dispute that flatpak/snap is your only option.