This does not always work under Windows (Networked APPDATA dirs)

[dragetd]

The environment variable can be broken on systems. We came across a setup with the users directory on a network drive H:\ and APPDATA not resolving to anything.

I am surprised myself how anything works on this system, but I guess Windows's own API which one is supposed to use does work:
https://stackoverflow.com/questions/5920853/how-to-open-a-folder-in-appdata-with-c

This is the same used by QT: https://code.woboq.org/qt5/qtbase/src/corelib/io/qstandardpaths_win.cpp.html

I'd recommend using this API call get the directory.