How to stop windows from shrinking to a smaller size?

And why has KDE made so many annoying nuisances like this (and tooltip popups and window shadows and window translucency, etc.) default settings rather than just letting anyone who wants those glitzy annoyances add them instead of forcing them upon everyone?

When is the windows shrinking and what are you doing when it happens?

You can always force a fix size for a window in systemsettings -> window behaviour -> window specific.