Flatpak aimed from the beginning to be distro-independent, and consequently the Freedesktop SDK isn’t a repackaging of Debian or Fedora or Alpine Linux, but something more like a DIY Linux From Scratch build. As an app user you don’t notice any of this, because it’s very well executed and apps just work. Again, it’s hard now to imagine a parallel universe where the main Flatpak runtime was Fedora in a trenchcoat, but perhaps that would have impeded the success of Flatpak. (Of course Canonical still built their own app store technology, but I suspect that Canonical re-inventing things is part of every parallel universe).

I still find this "distroless" talk funny. There's so little difference in whether the Freedesktop runtime is built like "Linux From Scratch" or assembled from Fedora packages. Fedora is also assembled like "Linux From Scratch". At the end of the day, they're both just taking upstream code and compiling it. Fedora just has an intermediary step of creating a package.

The only practical differences are the release scheduling, support length, and compile flags. In another world, the Freedesktop runtime could literally just be Fedora packages but with different compile flags that are less restrictive in terms of patents/codecs. And it would make almost no difference apart from the support length being different.