I was hoping that a standard gesture could trigger something else if there is an additional finger on the trackpad. But that doesn't seem to work. Is this a bug?
unfortunately that is not possible, the condition would always be false because 4 fingers are touching the trackpad, and even if you'd make the condition == 4, the the finger swipe would not trigger because 4 fingers are touching
I see. What might help is taking time into account.
So, the index finger of the left hand touches the trackpad... 1 second pause... then comes the 3-finger swipe with the right hand.
But that's needlessly complicated. A modifier will do the trick 
@Andreas_Hegenberg The setup below works
If one finger (left hand) is on the left side of the trackpad, you can execute swipe with your right hand (on the right side of the trackpad).
Unfortunately, this only works once. The finger (left) must be lifted repeatedly for the swipe to work again.
Do you see a way to make the swipe work as long as the finger remains on the trackpad? Thanks!
The finger on the left simulates pressing/releasing a modifier (shift). A swipe with the right hand can therefore be performed with or without a modifier.