When my new iMac was delivered, the only unsatisfactory I had was with the faulty trackpad. It can click, but can’t move the cursor at all! I sent it for servicing and got a replacement after a few days.

Anyway, this post isn’t about a new iMac with a faulty trackpad.

What happened is that when I use the new and working trackpad, I realized the 4 finger swipe up/down gestures were not working (therefore I can’t do Expose and Mission Control).

The fix is rather trivial:

Go to Preferences > Trackpad > More Gestures > Mission Control and change Swipe up with four fingers to Swipe up with three fingers.

Try it now and it should work.

Now, change it back to Swipe up with four fingers, and it works too!

Do the same trick for App Expose.

Finally, go to Point & Click to re-enable Three Finger Drag.