Scroll indicators hidden by default, never showing

In https://github.com/skiptools/skipapp-showcase navigate to the ScrollView playground, and scroll it.

Expected: There should be a scroll indicator on the right edge, like iOS
Actual: No scroll indicator

Even adding .scrollIndicators(.visible) doesn't help.

private struct VerticalScrollViewPlayground: View {
    var body: some View {
        ScrollView {
            VStack {
                ForEach(0..<30) { i in
                    Text("View: \(i)")
                        .padding()
                }
            }
        }
        .scrollIndicators(.visible)
        .refreshable {
            do { try await Task.sleep(nanoseconds: 3_000_000_000) } catch { }
        }
    }
}

The scroll indicator is still hidden.

Start with the ScrollView playground in the linked skipapp-showcase repository and reproduce the missing indicator using the shown .scrollIndicators(.visible) modifier. Trace the corresponding ScrollView behavior in skip-ui and compare it with the expected iOS behavior. Done means the indicator appears on the right edge when the playground is scrolled.