The ArcGIS Pro Layout Mode in the VSP Designer is not enabled. What might be the problem and how can I solve it?

Only the owner of the VSP Engine Tools (by default the user who installed the VSP Engine Tools) can enable or disable the ArcGIS Pro Layout Mode in the VSP Designer:

Alternately, adding or removing the VSP Engine Tools Portal item's 'Designer Pro' tag manually will make the tools accessible or inaccessible, respectively by adding or removing the 'Settings' menu option in the Designer.