In Web AppBuilder for ArcGIS, when using the Box, Dart, or Plateau theme, there is no option to open the attribute table from the layer drop-down list after configuring the Attribute Table widget to show the layer's attribute table.
In the Box, Dart and Plateau themes, the Attribute Table widget in the placeholder must be set as 'Shown' to activate the Open Attribute Table option in the Layer List widget. To make the Attribute Table widget available, users must place the mouse pointer over the widget's icon in the Widget tab and click the upper-right 'Show this widget' button. The widget icon appears in darker green after clicking. Go to the Layer List widget, and the option is available.
解决办法
Use another theme, such as the Billboard, Foldable, Jewelry Box, Launchpad, or Tab theme.