Main UI of all applications won't show all of a sudden

Hi there, for some reason my Impress won’t show it’s UI any longer. Means I load the app, it does show as active in my task bar but without any user interface.
It’s a strange issue because when I hit F5 the presentation will start, or blindly opening a dialog will show the dialog.
When I Alt-Tab between my running applications, Impress only shows a little box, Plasma also offers an overview screen as well, where Impress shows as icon only where all the other running applications will also show their minimized screen.

My assumption is that maybe there are some bogus screen coordinates in a settings file which prevent the main UI from showing, but don’t know where to look.

I was running LibreOffice fresh, but switched to still 7.3.6-2 after the issue occurred, unfortunately no effect.

I would appreciate any help as I need to finish up a presentation.

Edit: Just opened Writer and Calc, they now show the same issue? No ui

Operating System: Arch Linux
KDE Plasma Version: 5.25.5
KDE Frameworks Version: 5.98.0
Qt Version: 5.15.6
Kernel Version: 5.19.11-arch1-1 (64-bit)
Graphics Platform: X11
Processors: 8 × Intel® Core™ i7-6920HQ CPU @ 2.90GHz
Memory: 31,1 GiB of RAM
Graphics Processor: Mesa Intel® HD Graphics 530

It appears to me as if the window has a (near) zero size.
This is how I used to solve this issue on a gtk system:
When this window is active (positively reacts on shortcuts), hit Alt+Space bar which should trigger the windows menu having a “change size” command. In this mode, the 4 arrow keys pull the respective window border to either direction. You should practice this method with some application window that behaves normally.

@Villeroy That was a very good idea! In my case I used Meta-PageUp/PageDown to maximize/minimize. When minimizing I noticed that the window disappeared towards the right edge of my screen, and from there I was able to grab and resize the window.