I am using Neon, KDE Plasma version 5.27.3, Frameworks version 5.104. Somehow I have caused the desktop, icons on the desktop, the taskbar, and all windows to be magnified, as if I had selected a low resolution setting. I confirmed that the resolution setting is correct and that Global scale is set to 100%.
The screen image is the correct size during the boot cycle up until I log in. When I log in the desktop is magnified.
This happened while I was viewing a page in firefox and I pressed control + in order to magnify the selected image (in firefox). At least that is what I think I did. I have done this many times in the past to magnify an image, but only the image was not magnified, not the entire desktop. Control - usually reverses that action to reduce the image size.