Unity 7 uses three fingers double tap to do application switch (alt + tab), four fingers tap to open Dash menu.
Both gesture stops working after commit 0a4cf80a0066.
How are you handling all other touchpad gestures? This touch support was off by default and you have to disable tapping, scrolling, etc. to even get those touch events.
Also, given that this is the first complaint in the 3 years since we removed it, I don't think we'll bring that back.
I am not familiar how Unity7 handles multitouch gestures, so I contacted Unity7 developers about this issue, hopefully they can provide the information you need.
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