After upgrading from Fedora 30 to Fedora 31 all GTK based apps, like Evolution and Workrave, use bold fonts were they previously used non-bold fonts, and vise-versa. I’m using KDE as my environment. I’ve tried re-applying the settings in System Settings > Application Style > GNOME/GTK Application Style and then restarting the apps, but this did nothing.
EDIT: It seems to have something to do with the sans-serif variant of DejaVu fonts, since if I use fontconfig to blacklist the DejaVu Sans family everything works fine.
EDIT 2: The problem goes away if apps are run under a brand new test user.