KDE Plasma or KWin: configuration file damaged - how to reset?

*(see update below)* Using KDevelop 5.6.0 under Fedora with Plasma desktop. I pressed a wrong keyboard shortcut with Ctrl+Shift instead of Ctrl+Alt (or vice versa) and this "damaged" the bottom pane of the window where Konsole, compiling report, find across files, … display their results. Since I was in an editing task, I didn't notice the issue until I needed to activate Konsole. So I don't remember which key combination I typed. Now the "Build" button at top does nothing. If you press the Konsole button at bottom, "something" covers the concole pane and hides the edit window without resizing it. Even worse, when you start KDevelop, this bottom pane is used by nothing and you see the desktop through it. In short, KDevelop has become unusable. I suspect some configuration file has been damaged. I don't think any project conf file is involved (I've looked at *.kdev4* and all files in *.kdev4* without seeing unusual settings). I think that the general KDevelop UI configuration is somewhere else. I didn't find anything of interest in *~/.config* nor in *~/.kde*. I disinstalled and reinstalled KDevelop but, of course, this didn't purge any configuration file in user home directories. What can I do to recover KDevelop full functionality? Presently, it is reduced to Kate and I'm forced to pass commands in a separate console. **EDIT** KDevelop works like a charm under a different user account. The question above sums up to purging some hidden file(s), but which and where? I searched *~/.cache/* without success. **EDIT - 2020-12-09** Former title was: *KDevelop: bottom tool pane damaged* After a careful analysis of what is displayed on screen, I now think that the desktop manager (KDE Plasma) or window manager (KWin) configuration has been damaged because the windows lack their frame stroke. Also, the top window bar is a pure rectangle without the top rounded corners. Which file should be reset?