defaults write com.google.Chrome IncognitoModeAvailability -integer 2
defaults delete com.google.Chrome IncognitoModeAvailability
defaults write com.brave.Browser IncognitoModeAvailability -integer 2
defaults delete com.brave.Browser IncognitoModeAvailability
you get the idea...
note: when enabled you won't be able to access browser settings