Can I support supplementalActivityFamilies and also iOS17?

I have a live activity in my app, and beginning with iOS 18 these automatically appear on WatchOS and you can modify its appearance using supplementalActivityFamilies([.small]). My live activity supports iOS 17 and i would like to continue to support iOS 17 but would like to modify the appearance for iOS 18 devices. I figured this would be a simple if #available(iOS 18, *) but i run into an error

Branches have mismatching types 'some WidgetConfiguration' and 'ActivityConfiguration<OutageAttributes>'

    var body: some WidgetConfiguration {
        
        if #available(iOS 18, *) {
            ActivityConfiguration(for: OutageAttributes.self) { context in
                OutageActivityView(outage: context.attributes.outage, outageStatus: context.state, isStale: context.isStale, activityId: context.activityID)
            } dynamicIsland: { context in
                createDynamicIsland(context: context)
            }
            .supplementalActivityFamilies([.small])
        } else {
            ActivityConfiguration(for: OutageAttributes.self) { context in
                OutageActivityView(outage: context.attributes.outage, outageStatus: context.state, isStale: context.isStale, activityId: context.activityID)
            } dynamicIsland: { context in
                createDynamicIsland(context: context)
            }

        }
    }

Is there any way to conditionally support iOS18 features in iOS18 while keeping iOS17 target?

You can define the following extension:

extension ActivityConfiguration {
    func addSupplementalActivityFamilies() -> some WidgetConfiguration {
        if #available(iOS 18.0, *) {
            return self.supplementalActivityFamilies([.small])
        } else {
            return self
        }
    }
}

and apply it to your ActivityConfiguration:

var body: some WidgetConfiguration {
    ActivityConfiguration(for: OutageAttributes.self) { context in
        OutageActivityView(...)
    } dynamicIsland: { context in
        createDynamicIsland(context: context)
    }
    .addSupplementalActivityFamilies()
}