Issue
Some widgets in Service Portal designer display a "no preview available" message.
Resolution
Not all default widgets in Service Portal designer have the preview feature. The Service Portal form UI and Designer use the field has_preview, which defines whether preview data is available for the widget.
Check to see if the has_preview field value is set to false. If it is, this indicates that there is no preview data available for that widget to be shown in the designer.
To see the list of widgets that have the preview feature, add the field Has Preview via the form layout or on the list view of the widgets.
Note: Sign-in widgets do not have the preview feature available.