I don't get it, why reinstalling KaOS will getting worst font rendering when activated. Installing with KaOS 201810 with nonfree driver. Before 201808, font rendering works sharply. What I have to do?

KaOS is rolling, so it does not matter where you start, once you update from any ISO, the results are all the same.
So, a much clearer report is needed and why the re-install.
Did you start with a clean /home? What fonts are in use? When you state before 201808, did you never update such an install?

    demm Yes, I meant clean install with kept common folder on /home. I have replace my SSD with the new one. Last fresh install with KaOS 2018.06, still no bad fonts until reinstalling with KaOS 2018.10. On home partition, I kept on documents, music, video, downloads, and pictures. When enabling font antialiasing with usual settings, it produce bad font rendering on Dolphin, and also system settings.

      If you kept /home,, then make sure to test also with a clean, new user. As said, there is no difference once you do pacman -Syu with any ISO you install from. What KaOS does not control is what you do in your users /home.

      Thanks @demm , I think making it better from font antialiasing settings. I don't know why, but it happened since KDE Plasma 5.13 on Manjaro, also Neon. From font setting, since 5.13, unthick on checkbox "Exclude range from anti-aliasing", or don't giving check on it. So, font rendering back to normal and sharply.

      If you can pinpoint it to a Plasma 5.13 issue, then there should be a bug report for it, I will check.