The system date format is more about what you receive from and send to others. As you experienced in your experiment with bank statements. If in your region dd/mm/yyyy is the format used in communications, there’s little use to set your system preference to ISO. Sorting by date will be correct regardless.
Sorting text is another matter, of course. For that, I add the ISO-formatted date to the file name.
My experiment showed that it dow take into account the system settings. It does not even restarting DT. Immediately after changing the system settings, the result of the Scan Text changed.
So how do you explain that if the code doesn’t show it? Is it not that it using system settings which would normally not show in the code?
The automatically recognized document dates do not depend on the system settings but you used the Scan Text action to identify the desired date. Different case and different code.