The video referenced has the title DJI "Spark" not Mavic Air. I found out about the gimbal pitch tracking yesterday, when I forgot my USB to "C" cable.
I've got the button, but only when I'm connected via WiFi rather than via the controller. (Only noticed it as I'm charging the controller and waned to get some images of internal storage - one of the very scenarios where I use WiFi rather that the controller)