I've installed a desktop with buster to see if my FAI configuration was working. When I opened a xterm window I say that the font I use looks different than on stretch. It looks not that clean and a little more bold.

I've checked if the correct fonts were used using "xterm -report-fonts" which correctly showed

xos4-terminus-medium-r-normal--16-----*-iso10646-1

I'm setting this in my ~/.Xdefaults

Xft.hintstyle: hintfull

but on Buster the hintstyle (reported by xterm -report-fonts) was now 1 instead of 3. I found out that the package fontconfig-config has a now a new debconf question:

fontconfig-config fontconfig/hinting_style

I've set this to hintfull, but still no change. Then I found a very detailed description on FreeType Subpixel Hinting and Debian bug #867657.

The solution was to also set the variable

export FREETYPE_PROPERTIES=truetype:interpreter-version=35

buster