This is weird because when this problem occurred only fonts in Dolphin and KDE Settings were changed. But then after changing the default font every place in the system is affected. How can I fix this?
Try this settings instead
reboot after applying.
uncheck exclude range from and then click apply. whatever you do, do not re-open the font settings afterwards or the exclude range from anti-aliasing will be turned on again from 0 to 99 pt. there's actually a reproducible bug here.
Same problem here. Are there any fix?
Not in testing branch at any rate. It's an upstream KDE issue though so I'm sure it will be dealt with in the next Plasma Frameworks point release.