Update: This seems to be triggered by a fractional (> 1, but < 2, 1.4 in my case) Displays -> Scale -> Scale Factor setting (which is meant for HiDPI displays, and probably for people with sight issues), not "Force fonts DPI".
This upstream bug report seems to be related: https://bugs.kde.org/show_bug.cgi?id=373232
Update: This seems to be triggered by a fractional (> 1, but < 2, 1.4 in my case) Displays -> Scale -> Scale Factor setting (which is meant for HiDPI displays, and probably for people with sight issues), not "Force fonts DPI".
This upstream bug report seems to be related: https:/ /bugs.kde. org/show_ bug.cgi? id=373232