How can I detect Standby mode widget in TimelineProvider?

I want to check whether the widget is at Standby mode in TimelineProvider.

I thought showsWidgetContainerBackground == false means the widget is at Standby mode, referring to 'WWDC 2023 Bring widgets to new places'.

struct Provider: TimelineProvider {
    func getTimeline(in context: Context, completion: @escaping (Timeline<Entry>) -> ()) {

        let isBackgroundShown = context.environmentVariants.showsWidgetContainerBackground // Error: Cannot assign to property: 'showsWidgetContainerBackground' is a get-only property

        ...
        completion(timeline)
    }

...
}

But in TimelineProvider, I can't get context.environmentVariants.showsWidgetContainerBackground because it is get-only property.

This is because context.environmentVariants adopts @dynamicMemberLookup with WritableKeypath<EnvironmentValues, T>.

Is there any chance to detect the widget is at Standby mode in TimelineProvider? Is it possible or not?

Any suggestion would be very grateful. Thank you.