HiDPI support in KDE Plasma has been recently improved! I’m afraid what’s not improved is the procedure for using that. In this post I’ll detail the steps to use HiDPI with KDE if you have a high resolution display (for example, I have that in mylinux Dell M3800).
Remember that the settings you change will not be applied completely until you logout and login again into KDE.
First of all, you need to go in Settings , then
“ Display and Monitor ” -> “ Display Configuration “. If you scroll down you see a “ Scale Display ” button
Click on that and in the “ Screen Scaling ” dialog, drag the “Scale” in the middle, corresponding to a scale factor of 2 and press OK.
Then go back to the main page of Settings, select “ Font “, and force to the DPI font to 168 . (or even more if you want).
Apply the settings, logout and login again into KDE and you’ll enjoy your HiDPI display with a scale factor of 2, which basically means it will be usable
Be warned, KDE applications will look correctly, but there’ll still be other applications which might not have been implemented with HiDPI in mind… and they’ll still look horrible even with the scaling you set.