Widget Configuration UI "Add new item"

In the Explore enhancements to App Intents WWDC video at the 11 minute mark I see this UI in the Widget configuration.

My question is, how do I configure my Widget to use this UI in the intent configuration? I tried using all different sorts of types and am unable to reproduce it in my app

here is some test code that I was trying to use in order to get it to work

struct ConfigurationAppIntent: AppIntent, WidgetConfigurationIntent {
    static var title: LocalizedStringResource = "Test Sizes"
    static var description = IntentDescription("This is an example widget.")
    
    @Parameter(title: "Test Size")
    var sizes: [Size]
}

With Size defined as follows:

struct Size: AppEntity {
    let id: String
    let name: String
    
    static var typeDisplayRepresentation: TypeDisplayRepresentation = "Size"
    static var defaultQuery = SizeQuery()
    
    var displayRepresentation: DisplayRepresentation {
        DisplayRepresentation(title: "\(id): \(name)")
    }
    
    static let small = Size(id: "1", name: "Small")
    static let medium = Size(id: "2", name: "Medium")
    static let large = Size(id: "3", name: "Large")
    
    static let allSizes: [Size] = [small, medium, large]
    
    struct SizeQuery: EntityQuery {
        func entities(for identifiers: [Size.ID]) async throws -> [Size] {
            Size.allSizes.filter { identifiers.contains($0.id) }
        }
        
        func suggestedEntities() async throws -> [Size] {
            Size.allSizes
        }
        
        func defaultResult() async -> Size? {
            try? await suggestedEntities().first
        }
    }
}

This results in the following experience:

And when I update the @Parameter line to be I get the following:

@Parameter(title: "Test Size", size: [.systemSmall: 1, .systemMedium: 2, .systemLarge: 4, .systemExtraLarge: 4])

Which is still not what I am looking for.

Thanks!

Widget Configuration UI "Add new item"
 
 
Q