It's an issue that's been discussed here, numerous times, and the only advice that can be found is to delete "config.xml" at "/Users/${USERNAME}/Library/Preferences/DefendersQuest" so the game starts with default settings.

However, all the paths are different now — and seems like it's a choice of the game, not a consequence of newer MacOS versions doing things differently.

The correct path for MacOS is:
and the file to be deleted is named options.xml now