Touchpad users can pinch to zoom in/out horizontally on the arranger. Adding vertical pinch to zoom would allow the height of a track to be changed more fluidly than dragging and would be consistent with the behaviour of the horizontal pinch gesture.
(Describe your feature request in a way that a Bitwig newcomer can understand. Optionally, fill the sections below. If you don’t have time now it’s ok, you or others can work on this draft later. For more information, see Writing a good feature request)