Indeed, it's a regular 1980x1080px Monitor.
It seems to be an issue with the Qt libraries shipped with Calibre.
Although I don't use many Qt applications (and most of them are still on Qt4), the native Qt5 diagnosis on my system returns:
Code:
$ qtdiag-qt5
[...]
Screens: 1, High DPI scaling: inactive
# 0 "eDP1" Depth: 24 Primary: yes
Geometry: 1920x1080+0+0 Available: 1920x1053+0+27
Physical size: 280x160 mm Refresh: 60 Hz Power state: 0
Physical DPI: 174.171,171.45 Logical DPI: 96,96 Subpixel_None