"6. Click on Open from folder and select your Documents folder there. Confirm that works as expected and displays the name and contents of one of the text files in Documents."
It's because in step 6 the user explicitly selected the Documents folder.
The app can access the Documents folder because the user chose that directory in the native file browse dialog during the same run of the app. IMO that's a reasonable trade-off.
> during the same run of the app
Is this part true? The article's fix involves running a command and rebooting the computer. If restarting the app was sufficient, surely you wouldn't need the command/reboot?
The problem is that this given permission doesn’t show in Files & Folders, and after turning it on and off there it still persists. The only way to revoke it is using some CLI command and restart the computer.