PROBLEM
The Description option of a layer is unavailable in Map Viewer.
The layer is a feature collection and not a hosted feature layer. Feature collection layers are stored in the web map, and the description information is not available.
Save the layer as its own item so it becomes a hosted feature layer. Refer to ArcGIS Online: Save layer for more information on saving the layer.
When saving a feature collection as its own item, the data is retained with the feature collection item and not stored as part of the web map. Refer to ArcGIS Online: Feature collections for more information.
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