During upgrade I noticed, that noto emoji are again giant, despite 10-scale-bitmap-fonts.conf enabled. It took a while until I decided to look if there are any errors in terminal, there is it:
Fontconfig error: "/etc/fonts/conf.d/10-scale-bitmap-fonts.conf", line 1: no element found
As expected media-libs/fontconfig-2.13.1-r2 install a perfectly functioning /etc/fonts/conf.avail/10-scale-bitmap-fonts.conf which like any other file in that folder can be symlinked to from fonts/conf.d, to activate that particular fontconfig file. This is normally handled by eselect fontconfig.
Things to do here:
1) if the /etc/fonts/conf.d/10-scale-bitmap-fonts.conf is not a symbolic link to the corresponding conf.avail/ file (e.g. a regular file or a symlink pointing to the wrong file), then that's almost certainly a mistake and can be easily fixed by replacing it with the proper symbolic link
2) if the symbolic link is correct, then clearly conf.avail file has either been accidentally edited/replaced with an empty file or it may have been lost to filesystem corruption. The immediate solution is to re-install media-libs/fontconfig and run dispatch-conf to update it and other files that may have changed but it's __very important__ to figure out if the file was accidentally cleared or if silent data loss is taking place!
Thanks, that helped.
However, I typed dispatch-conf rather voluntary, without making clear if need to run if was mentioned. Now check is impossible, because dispatch-conf ate some part of output (using urxvt, apps using second screen like mc or recent bashmount are fine).