[otterlicious]

I want to completely disable clipboard management so it wouldn't remember clipboard history (which is a security issue) and wouldn't clear the clipboard as soon as I close the window (extremely inconvenient - I often want to open a window just to copy something, close it and paste that somewhere else). But I could never find how.

If you disable clipboard management on X11 then the clipboard goes away when the application does - that's how X11 works and the whole reason clipboard management exists.

If you don't want it to keep any history but the most recent item, then just disable that.