i would expect a directory beside the .plan file which contains backup versions of said plan file
Dang, sorry to hear that it's not working; I think a separate thread for the bug report would be helpful. Please include relevant information, like OS, if you're running MasterPlan through the itch app or not, the log file from MasterPlan's directory, and the project file itself.
Also, just to confirm, the currently implemented system is to back up the project by saving it again periodically (every x minutes) with a different filename in the same directory as the project file's original save location. If you've never saved your project, lack the rights on your OS to save a file in that location, or aren't waiting for the backup timer to elapse, then that would explain why the backup doesn't work. Also, while MasterPlan should work just fine regardless of the project's filepath, it would be helpful to know if the project file's path contains special characters.