Unlike Gnome, KDE do actually care about their users, not just about themselves.

It's hilarious how, despite KDE apps being broken on every DE that isn't plasma, people will still find a way to blame Gnome for it.

Contrarily to KDE, Gnome has managed to make sure that libadwaita apps look and work just like they're supposed to and how its shown on the screenshot in the app store. You might not like the theme, but at least you knew what to expect before downloading, whatever distro you are on.

It's great that KDE finally managed to fix their app so that they come with everything it need to function properly. People might be able to use them now on other DEs.

Man this Missinformationen is hard to squash. Yes Flatpaks absolutely share libraries. These are called runtimes and are shared between all the Flatpak apps that use the same version of it. You will only get more than one version of a given runtime if some apps need this other version. For most runtimes that I know of, most only have 2 currently maintained versions, so I almost never get more than that on my system (and when I do, app devs tend to update their apps shortly after so that they're using a maintained runtime). For example on my system where I mostly use GTK apps, I only have two versions of the Gnome runtime (44 and 45). And even when you have more than one version of a runtime, they get deduplicated, so even runtimes share parts between them.

If you're interested here is an article about it.

As other have pointed out, saying that "no dependencies are shared" is a very missinformed take, given that sharing dependencies as runtimes is an integral part of Flatpak's structure. But what makes it even funnier and more obvious that you don't know what your talking about, is that you than cite Nix as something you "vastly prefer" when Nix actually deals with dependencies in a very similar way to Flatpak. From the official site:

You can have multiple versions or variants of a package installed at the same time. This is especially important when different applications have dependencies on different versions of the same package — it prevents the “DLL hell”.

In both Flatpak and Nix, apps will only download a different version of a dependency when they need it. This ensure that, instead of breaking, the app will work the same on any system (be it an old stable Debian or a bleeding edge Arch system), without requiring devs to create monkey patches that they have to maintain as things evolve. It has the potential to immensely reduce the burden on app devs and maintainers, and make it a lot easier to make apps for Linux.