This is what I got after copying that command in the terminal:
softwareupdate --fetch-full-installer --full-installer-version 11.6.8
Downloading and installing 11.6.8 installer
SUPreferenceManager: Failed to set object of class: __NSCFConstantString for key: LastRecommendedMajorOSBundleIdentifier with error: Error Domain=SUPreferenceManagerErrorDomain Code=1 "(null)"
SUPreferenceManager: Failed to set object of class: __NSCFConstantString for key: LastRecommendedMajorOSBundleIdentifier with error: Error Domain=SUPreferenceManagerErrorDomain Code=1 "(null)"
Install failed with error: Update not found