X is the client and server for rendering pixels on to a screen, which is mapped to one of more monitors. It provides the most basic, bare bones way to draw a window to the screen, and that’s about it.
It’s not even a GNU/Linux thing, X predates Linux, it’s more of the standard system to draw a window on Unix-like systems.
X11 apps are GUI apps uncontrolled by/unaware of a desktop environment, theme engine, or window manager. They appear in a minimalist, maybe even brutalist, aesthetic. You can launch a single X11 app from the console, and the resulting window will be your entire graphical display/instance, returning you to the console after the program terminates execution.
Maybe another way to think about your question might be, think of X vs Wayland.
> You can launch a single X11 app from the console, and the resulting window will be your entire graphical display/instance, returning you to the console after the program terminates execution.
Is this not possible with GUI apps using e.g. Qt or Electron?
It’s not even a GNU/Linux thing, X predates Linux, it’s more of the standard system to draw a window on Unix-like systems.
X11 apps are GUI apps uncontrolled by/unaware of a desktop environment, theme engine, or window manager. They appear in a minimalist, maybe even brutalist, aesthetic. You can launch a single X11 app from the console, and the resulting window will be your entire graphical display/instance, returning you to the console after the program terminates execution.
Maybe another way to think about your question might be, think of X vs Wayland.