ios Shortcuts: get index of selected list item

Based on the comments, this Apple Support site held the answer. Use "Set Name" to get the value:

To set a custom name for an item that an action outputs, such as an image in the Get Latest Photos action, place a Set Name action in between the Get Latest Photos action and the Choose from List action. When the shortcut is run, the custom name (rather than the default name, such as “IMG_0365”) is applied to the image output from the Get Latest Photos action.

If you use the Choose from List action with the Dictionary action, all of the keys in the dictionary are displayed when you tap “Add new item.” For each key you select, such as Number, Boolean, or Array, the corresponding values are passed as output.