Yes, I can give a clear description: the Mac version has no mta files, it's a format that is used in the Windows version and not available on the Mac.
Instead, it stores the preferences (including action groups) in macOS User Defaults which you can read via Terminal.app and the command
defaults read app.mp3tag.Mp3tag
So, if you're using for a quick and easy way to import your actions from Windows, it's unfortunately not possible. See also FAQ → Can I import data from Windows.