In the Windows operating system, it is common to see that you can use three or four fingers on the touchpad to perform an action. 

I don't know if it's related to Windows or if it's a manufacturer's software (like "Smart Gesture") that allows this. I suggest that we add a default disabled possibility to implement it under Plasma like Asus Smart Gesture.

We can think about the actions that should be done with three fingers and four fingers, but I would start with this type of action:
- three fingers: Run the application launcher
- Four Fingers: Open notifications.

Of course, what I said can be adapted.
What do you think about it?