Adding Items

Keep the items in @State and the list updates whenever the array changes. A text field and a button are enough to add items:

@State private var items = ["Milk"]
@State private var newItem = ""

var body: some View {
    VStack {
        TextField("New item", text: $newItem)
        Button("Add") {
            items.append(newItem)
            newItem = ""
        }
        List(items, id: \.self) { item in
            Text(item)
        }
    }
}

items.append(newItem) adds the typed text to the array, and newItem = "" clears the field for the next item. Because items is state, the list shows the new row right away.

A button can be disabled while the field is empty: .disabled(newItem.isEmpty).