ScrollView and prefersDefaultFocus currently incompatible?

Yes, seems like since you wrap up HStack to ScrollView prefersDefaultFocus won't work correctly after that. I have a similar issue and can't get it to work for tvOS 14. Nevertheless, it works well with iOS 15 using @FocusState. So if you don't need tvOS 14 support you can use that approach. Here are my observations of the issue. What I try to achieve is set focus on the last item(10) if you press down on items 7 or 8. If I'm not wrapping up LazyVGrid into ScrollView everything works as expected. But as soon as I wrap up LazyVGrid into ScrollView when I press the down button on those items it always gets focused on the first item. Here is my code example and screenshot.

struct ContentView: View {
    @Namespace var focusNamespace
    @Environment(\.resetFocus) var resetFocus
    @State private var defaultFocusIndex: Int = 0
    @State var items = ["1", "2", "3", "4", "5", "6", "7", "8", "9", "10"]

    let columns: [GridItem] = Array(repeating: .init(.flexible()), count: 4)

    var body: some View {

        ScrollView() {
            LazyVGrid(columns: columns) {
                ForEach(items, id: \.self) { item in
                    Button {

                    } label: {
                        ItemView(title: item)
                    }
                    .prefersDefaultFocus(item == items[defaultFocusIndex], in: focusNamespace)
                    .onMoveCommand { moveCommandDirection in
                        guard let index = items.firstIndex(where: {$0 == item}) else {
                            return
                        }

                        if moveCommandDirection == .down, index >= items.count - columns.count {
                            defaultFocusIndex = items.count - 1
                            resetFocus(in: focusNamespace)
                        }
                    }
                }
            }
            .focusScope(focusNamespace)
        }
    }
}

And here is the working solution for tvOS 15:

struct ContentView: View {
    @FocusState var focusedItem: String?
    @State var items = ["1", "2", "3", "4", "5", "6", "7", "8", "9", "10"]
    let columns: [GridItem] = Array(repeating: .init(.flexible()), count: 4)

    var body: some View {
        ScrollView() {
            LazyVGrid(columns: columns) {
                ForEach(items, id: \.self) { item in
                    Button {

                    } label: {
                        ItemView(title: item)
                    }
                    .focused($focusedItem, equals: item)
                    .onMoveCommand { moveCommandDirection in
                        guard let index = items.firstIndex(where: {$0 == item}) else {
                            return
                        }
                        if moveCommandDirection == .down, index >= items.count - columns.count {
                            focusedItem = items.last
                        }
                    }
                    .padding(.bottom, 8)
                }
            }
        }
    }
}

If you have any workaround for tvOS 14 I'll be appreciated it.

Does this approach still work for you? I try it on a tvOS 17 simulator, and it always resets to the first item, even if I say that the default focus index should be 2.