It seems that I can change the font size of panels by adding,
to “kritarc”. But this was never mentioned anywhere except on some user posts on the Internet. That is, normal users would never know that this value even exists.
Can I get the list of all such hidden entries? I would like to change the font size of the main menu and dialogues, because they are too small. I cannot find any way to do so within the GUI, so I am looking for a way to achieve this using “kritarc”.
That is actually the only special font definition that Krita reads; the rest is taken from the system. If the fonts are too small, enable HiDPI and play with your OS/Desktop’s display scaling. We don’t have a full list of all possible entries either, it tends to grow and grow. A large number, but not all, are defined here: https://phabricator.kde.org/source/krita/browse/master/libs/ui/kis_config.cc — but not all of those entries are still in use.