Few Nintex action items are disabled at the central administration.
Please follow the below steps to find which action items are enabled at the site collection.
Site collection>site actions>Nintex Workflow>Manage allowed actions>
Display all action items which are enabled at site collection level.
If in case, we need to enable the action items which are disabled at the central admin: Click “Switch to admin view – show all actions” and “click Stop inheriting actions” button.
You will get the all Nintex action items, which are available at the central admin. We can check or uncheck the action items accordingly.