That’s the domain of a window manager. It’s touched on in the article, but going into detail about the edge cases would require detours into user space window manager choices and even preference settings.
I'm not even talking about edge cases. It doesn't even give a high level. It just treats wayland and x as big black boxes and does not explain what happens inside of them.
I'm was expecting a full end to end analysis of how inputs travels through the system. A proper analysis shouldn't just examine both ends of the system, but follow what happens during each step of the process.