If the XDG_DATA_HOME environment variable is set then the root certificate should be generated in ${XDG_DATA_HOME}/minica.

https://specifications.freedesktop.org/basedir-spec/basedir-spec-latest.html

On macOS it should go into ~/Library/Application\ Support/com.jsha.minica (XDG_DATA_HOME takes preference though).

https://developer.apple.com/library/archive/documentation/FileManagement/Conceptual/FileSystemProgrammingGuide/MacOSXDirectories/MacOSXDirectories.html