It would be nice to allow(again) users to change particular font size in decimal numbers. The funny fact is that it can be done only by Adjust all fonts. Reproducible: Always
The issue is in the Qt font dialog, which the frameworks-integration plugin does not change to the KDE font dialog. I am not sure if that should happen; if not it would be a Qt issue.
Upstream dialog seems to only accept integers, so if there's a bug please file it upstream at https://bugreports.qt.io
The fonts KCM in systemsettings has been changed to use KFontChooserDialog, which allows setting decimal font sizes, see D27808. If I am reading the release schedules[1] correctly, this change should be in plasma-desktop 5.19. [1] https://community.kde.org/Schedules/Plasma_5
Awesome!