Created attachment 128013 [details] Plasma Discover font rendering SUMMARY Fonts in applications that use Kirigami have very blurry font rendering. STEPS TO REPRODUCE 1. Set system font to Noto Sans 9 2. Open a Kirigami-using application such as KDE Connect SMS or Plasma Discover OBSERVED RESULT Fonts render terribly EXPECTED RESULT Fonts render well SOFTWARE/OS VERSIONS KDE Plasma Version: N/A (XFCE 4.14) KDE Frameworks Version: 5.68.0 Qt Version: 5.12.8 ADDITIONAL INFORMATION My system is based on XFCE 4.14 (Xubuntu 20.04), though after setting the QT widget style to Plasma things still look the same. I haven't tested many other system fonts, but none of the ones I tested looked fully proper.
I can't distinguish any "super blurry fonts" in your screenshot. Can you attach a screenshot of a non-Kirigami-based QWidgets app like Golphin or Gwenview that shows how you think the fonts should look?
Created attachment 128063 [details] Comparison of font rendering Here's a screenshot that shows the font rendering in various applications. From left, the first is Thunar, GTK-based, and has the (IMO) best font rendering. The next is a qt5 app (qt5ct), which has imperfect but decent font rendering. On the right are two Kirigami-based applications, with very noticeable font blurring.
Ah, I see it now. I don't think I ever would have if you hadn't pointed it out though! Doesn't looks like Plasma is affected, so it's not all QML software that's affected.
I can't reproduce this, but it looks like hinting is turned off in Discover (QML). What's in the .config/fontconfig folder? Btw you should avoid using qt5ct as it tries to take over Plasma theming and doesn't do as good of a job as Plasma. It's precisely known for messing up QML apps. You could also try removing it to see if it changes anything.
Yeah this should be a qt5ct bug. I just reproduced it by setting the QT_QPA_PLATFORMTHEME to qt5ct. It insists on doing its own font rendering for QML and disobeys the Plasma setting.