When a font, which is selected in kde-gtk-config, is available from two or more sources, the app saves its name into the configuration file with a suffix, and this notation seems to be not recognized by GTK resulting in "SansSerif" font being used instead of the selected one. Example: gtk-font-name=Cantarell [ABAT] 9 Removing "[ABAT]" satisfies GTK and it uses Cantarell then. Reproducible: Always Steps to Reproduce: 1. Find or install a font, available in two variants with different foundry names or one with foundry name and the other one without. 2. Select this font in kde-gtk-config and save configuration 3. open ~/.config/gtk-3.0/settings.ini and notice foundry name or '[unknown]' in the gtk-font-name value. 4. Launch a GTK 3 application. Actual Results: The application uses "SansSerif" font for UI. Expected Results: The selected font is used for UI.
Fixed by https://cgit.kde.org/kde-gtk-config.git/commit/?id=94732eb8d6ee54573a4476e7b036808ac9907ba0 in Plasma 5.18.