I clicked the Chain icon button to map a field, but the needed field is not in the drop-down list. What can I do?

The drop-down list fully depends on the columns available in the view of your source list/library. Therefore, if a particular column is hidden in a particular view of the list, and you connect a ShortPoint element to this view, this column will not be visible in the Items Mapping drop-down. Therefore, please check the SharePoint list/library view. Detailed instructions in this article.