Default cache directory on MacOS shall be set to ~/Library/Caches/Duplicacy not ~/.duplicacy-web/cache. It’s a bad form to litter with temporary data in users home.
Windows also has dedicated location for cache somewhere in AppData directory, don’t remember the correct path.
But that’s the start really. macOS (as does windows) has dedicated locations for application data and preferences; there really should not be anything under user’s home root. See ~/Library/Preferences, ~/Library/Application\ Support. Even dumping the current ~/.duplicacy-web (minus caches) to ~/Library/Duplicacy would be a step in right direction.