Just installed plasma 5.16.3 in fedora30 using copr repo mkyral:plasma-unstable. Seems to work ok, until you play around with the new systemsettings. Then, without notice, the font aliasin stops working... What happens is, that in fonts, anti-aliasing is still enabled, but the option 'exclude range from anti-aliasing' is suddenly activated. And, because the default values are from 0x to 99px, effectively all UI anti aliasing is gone. Workaround: define another range, like 0px to 1px because it will get enabled anyway some time later on (did not find out when for now). Switching this option to 'off' just doesn't work (only temporarly)
*** This bug has been marked as a duplicate of bug 409518 ***