Prior to version 9.1.1 on small screens (below 720 pixels), Produce would cause the left-hand wizard navigation menu to disappear to save screen space.
As of 9.1.1, however, the navigation menu will collapse to a drop-down list, accessible from the top navbar (via a 'three-lines' icon). Once shown, it can be hidden again by clicking on the icon once more.
The icon will display in portal mode (enabled with the "?portal=1" parameter on the URL string) for screens of the relevant size.
The icon will not display if the form has the 'Hide Navigation Page' publish option enabled.
small-screen navigate produce wizard