Bump - apologies. Something has changed here. Previously, middle-clicking in empty space brought up the windows “scroll anywhere” tool (real name not known to me) but now it does a panning hand.
The difference is that the scroll tool allows a gradual pan with no mouse movement (leave the mouse to one side of equilibrium and the system will continually scroll in that direction)
Now it requires multiple click-drag movements to scroll. Less ergonomic for me.
Edit: Since space bar and right click already do the hand thing, is there any harm putting middle-click back how it was? Worth asking…