In Debian 10 stable with KDE changing the scaling under the display settings has a lot of bugs.
For example the tabs in the bottom panel are too large and have a font-size that's much too large so that only very few open windows are shown there. Furthermore, the text-size of many buttons is too large for the buttons, text and icons are unaligned in the left sidebar in dolphin and the space between icons on the desktop is too large. There also are some other problems. Some of these might be solvable with some other display settings (like adjusting the font size) - I haven't tried it much because I prefer the original scale and instead change the scale within apps as needed.
How to increase the maximum zoom of Qt apps like the dolphin file explorer or GTK apps like lutris?