Testing d3-zoom (e.g. https://observablehq.com/@d3/zoom-canvas-rescaled or any other) on an iPad, a dbltap doesn't trigger x2 zooming—but a triple tap does. With the pencil it's never triggered, no matter how many "taps".

(On the iPhone dbltap works. )

I'm investigating but it would be nice if someone could confirm or infirm this observation.