Viewing the Overview immediately when opening the game worked fine this time. I have been able to trigger the error again, however. After pressing 1, attempting to load the "windows example" Save Data, which produces a different error:
An error occurred while loading your Save Data. Press any key to return to the Title Screen. If you're trying to migrate Save Data from an older version of PyNori, please run it through the Save Update Utility found at https://shirley-xml.itch.io/pynori-suu.
When attempting to view the Save Data Overview after this, the serious error occurs. I've also found that a similar error appears when attempting to access the options menu at this point.