Kwin is the default window manager for the K desktop environment. In
the near future, I will explain in further detail what a window manager
is and what a desktop environment is.
The important information
right now is the fact that kwin is your guardian against UI harassment .
especially violent focus stealing and oppressive Z-sorting of
application windows.
In this post, i will describe in detail the benefits of using kwin in everyday desktop use.

As
stated before, the sole and highest authority of the desktop is the
user. No program may disturb the order established by the user without
express order by the user.
Focus stealing protection
this
video shows what happens if you tell the terminal emulator application
to open a new window. first, without focus stealing protection, and then
with kwin focus stealing protection
the blue window decoration indicates focus.
https://www.youtube.com/watch?v=A0oQvCmn81Q
The kwin settings can be reached through the window menu or kde settings -> window behavior
window z-ordering
Another advantage of the Kwin window manager is z-ordering for the windows.
Applications automatically making themselves always on top
A window wants to force itself to be always on top? kwin can put a stop to this outrageous insubordination.
To
disable an application from forcing itself on top, click on the
application icon/window button on the top left corner of the window's
window decoration. Then go to
more actions > and click
special application settings
the window for editing application-specific settings will open. Go to the
Arrangement & Access tab.
Enable the
Keep above control. In the drop-down menu, select
Force, and click the radio button
No
https://www.youtube.com/watch?v=u4-XkXd_A8o
congratulations.
You have prevented this application from staying always on top. Not
even setting the always-on-top flag from the window manager settings
under
more actions will be able to force this window on top
now. you can choose to edit this setting at any time. If you, however,
want to choose the always-on-top setting from the application window
menu manually, you should select
remember or
apply initially from the drop-down menu.