Are apps on one linux desktop environment compatiable with another desktop environment？

Question

Are apps on one Linux desktop environment compatible with another desktop environment? My distribution is Arch, and I am using Plasma 5 DE. When I install and run apps that are said to be built for another DE such as Gnome or pantheon, the apps run but the GUI seemed a bit messed up. For example, the panteon mail application lack the top system menu (which allows you to drag, close, or minimize the window) and Nylas N1 mail application's top system menu shows X11 rather than the normal KDE style menu.

I understand that many apps with GUI are based on GTK+, Qt, or Electron nowadays. But to me, it seemed like they are all compatible to X11 and there is no reason why these apps do not function properly on another DE based on X11.

Answer 1

Regarding the second part of your question; the one error in that line of thought is the fact that all these different GUI libraries run on X11 is irrelevant. The problem is that your plasma DE primarily uses the Qt environment and many others, like Gnome, use some version of GTK.

So, applications built on libraries different from your primary DE will usually run so long as the necessary libraries are installed, but the application may not appear as it was intended and may exhibit unexpected behavior. It's your call whether you consider this to be "compatible" or not.

Answer 2

As far as I understand, the X server handles the drawing of the environment but does not make the rules as to how the windows or desktop environment is drawn. The logic that tells the X server how to draw the windows would reside within the desktop environment's programming (or within the libraries it calls such as libqt*). As a result, if a specific desktop environment does not properly interpret how to setup the window (ie. it was designed for a different DE or uses widgets that are not native to the DE - such as GTK+ on KDE), it may not give the X server proper instructions on how to draw the window.

The underlying widget set for KDE is Qt and the underlying widget set for Gnome-based DEs is GTK+: so not all programs built for one DE may function as intended on another.

If you're using KDE newer versions will have a way to change how KDE handles GTK applications (System Settings -> Application Style -> Gnome Application Style (GTK)):