Titlebars are a total waste of space, especially on maximised windows. Here is, in my opinion, the best way to get rid of them.
Hiding window borders (including titlebars) is easily done on Plasma on a per-window basis using the Window Operations Menu, default shortcut: Alt+F3, or on a per-application basis, by setting Window Rules. But that is quite slow and cumbersome, as you would have to do it manually for every window. Not good. You can also set a keyboard shortcut to hide and show window borders. Better, but you still have to do it manually.
Fortunately, there also exists a hidden setting in KWin to automatically hide titlebars and window borders on maximised windows. To apply it, edit the following file:
~/.config/kwinrc
Find the section [Windows] and add BorderlessMaximizedWindows=true under it. It should look something like this:
[Windows]
BorderlessMaximizedWindows=true
Log out and log back in. Open any application and maximise it to see the effect.
This way you have the best of both worlds: floating windows still have titlebars and fancy shadow borders and whatnot, and maximised windows have none of that clutter, letting you utilise your screen real-estate to the fullest.
Depends on what you have as a shortcut to move and resize your windows. One way I do it is by using Meta + left , and drag to move the window and Meta + right , and drag to resize it.
Some users have Alt instead of Meta. You can change that in
System Settings → Window Behaviour → Window Actions → Inner Window and Frame Actions → Modifier key
You can also set various KWin keyboard shortcuts under:
System Settings → Shortcuts → Shortcuts → Kwin
If you want it only on a specific application, and not in general, you can set a rule for that application, by focusing on a window of that application and
Alt+F3 → More actions > → Configure Special Application Settings…
“Lower” sends your focused window below other windows without losing focus. “Raise” brings it to the top. “Toggle raise and lower” does either of these things, depending on whether the window is on top or not.
This is not the same as “Keep window above others”.
Just play around with it a bit and you’ll figure it out.