Ios `Task` 在内部调用异步函数时阻塞主线程

我有一门ObservableObject课和一个快捷界面.当点击一个按钮时，我会创建一个Task，并从中调用populate(一个异步函数).我原以为这会在后台线程上执行populate，但整个UI会冻结.这是我的代码:

class ViewModel: ObservableObject {
    @Published var items = [String]()
    func populate() async {
        var items = [String]()
        for i in 0 ..< 4_000_000 { /// this usually takes a couple seconds
            items.append("\(i)")
        }
        self.items = items
    }
}

struct ContentView: View {
    @StateObject var model = ViewModel()
    @State var rotation = CGFloat(0)

    var body: some View {
        Button {
            Task {
                await model.populate()
            }
        } label: {
            Color.blue
                .frame(width: 300, height: 80)
                .overlay(
                    Text("\(model.items.count)")
                        .foregroundColor(.white)
                )
                .rotationEffect(.degrees(rotation))
        }
        .onAppear { /// should be a continuous rotation effect
            withAnimation(.easeInOut(duration: 2).repeatForever()) {
                rotation = 90
            }
        }
    }
}

结果:

按钮停止移动，然后在populate结束时突然弹回来.

奇怪的是，如果我把Task移动到populate本身，go 掉async，旋转动画就不会断断续续，所以我认为循环实际上是在后台执行的.然而，我现在得到了Publishing changes from background threads is not allowed的警告.

func populate() {
    Task {
        var items = [String]()
        for i in 0 ..< 4_000_000 {
            items.append("\(i)")
        }
        self.items = items /// Publishing changes from background threads is not allowed; make sure to publish values from the main thread (via operators like receive(on:)) on model updates.
    }
}

/// ...

Button {
    model.populate()
}

结果:

如何确保我的代码在后台线程上执行？我想这可能与MainActor有关，但我不确定.