The default font for KDE is Noto Sans 10 pt. 10 pt is really small and the font is fairly wispy at that size. Increasing to 11 pt offers a vast increase in usability and reduction in eyestrain.
To keep the relative size differences, every other font should likewise be increased by 1 pt.
This looks really, really good:
{F5688113}
Compare that to the default settings:
{F5688114}