See:
Keyboard Maestro cannot see the future, so it cannot tell after you tap once, whether you will or will not tap a second time.
the only way to do this would be for the first tap once trigger to wait and see what happens later and only trigger if the tap twice does not happen. You can do this yourself, something like:
Tapped Once:
- Set variable Tapped Twice Fired to 0
- Pause long enough to be confident you have not tapped twice (3 times the double click interval)
- If variable Tapped Twice Fired is 0
- Do stuff
Tapped Twice:
- Set variable Tapped Twice Fired to 1
- Do stuff