Using 2 Finger Click + Drag to rotate the Viewport camera does not provide the behavior that is described in the documentation. Instead of rotating the camera in place as the documentation describes, the camera instead pans left, right, up, and down. It is unclear if the error is in the camera functionality or in the documentation.
RESULT:
Using 2 Finger Click + Drag to rotate the Viewport camera results in the camera panning left, right, up, and down.
EXPECTED:
Using 2 Finger Click + Drag to rotate the Viewport camera results in the camera rotating up and down as well as left and right, and not moving at all.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-56123 in the post.