After updating to Plasma 5.27.1 TW 20230224, the application font sizes became
tiny, both in KDE applications such as kate and konsole and non KDE
applications such as google-chrome and jetbrains pycharm. 

On the other hand the size of the window decoration fonts, panel fonts, and
desktop widgets remained unchanged.

I attempted to use Settings to change the default font sizes, but then window
decoration fonts, panel fonts, and desktop widget fonts became huge.

I have one 27" 4K monitor and one 1920x1200 monitor.  Perhaps the 4K monitor
has something to do with it.  I run the 4K monitor unscaled in KDE and use
xrandr to scale the 1920x1200 display by 1.75 (which is fine for text):

xrandr --output DP-4 --auto --output DP-0 --auto --scale 1.75x1.75 --right-of
DP-4

I've reverted to 5.27.0 which has fixed the issue, although I should note that
since Plasma 5.27.0.  I've seen the odd problem with google-chrome switching to
tiny fonts, and this was resolved by logging out and starting a new session.

I should probably also note that kscreen2 is disabled (to avoid the hot-plug
actions associated with turning off DisplayPort screens).

I tried to log this bug before, but it seems to have disappeared - apologies if
this appears as a duplicate.