The Guid() Arcade function does not evaluate in a smart form in Map Viewer (ArcGIS API for JavaScript 4.x).

Additional Information

Workaround

1. Open the feature layer's Data tab from the item details page.
2. In the table view, click the name of the new field, then click Calculate.
3. Click Arcade.
4. Type in the expression: return Guid().
5. Click OK.
6. All records are updated as expected.
7. Alternatively, add the feature layer to a map in ArcGIS Pro, run the Feature Class To Feature Class tool to create a local copy of the feature layer, run the Add Global IDs tool, and overwrite the existing feature layer.

Steps to Reproduce