Layout in SwiftUI with horizontal and vertical alignment

not an expert here, but I managed to achieve the desired layout by (1) opting for the 2-VStacks-in-a-HStack alternative, (2) framing the external labels, (3) freeing them from their default vertical expansion constraint by assigning their maxHeight = .infinity and (4) fixing the height of the HStack

struct ContentView: View {
    @State var text = ""
    let labels = ["Username", "Email", "Password"]

    var body: some View {
        HStack {
            VStack(alignment: .leading) {
                ForEach(labels, id: \.self) { label in
                    Text(label)
                        .frame(maxHeight: .infinity)
                        .padding(.bottom, 4)
                }
            }

            VStack {
                ForEach(labels, id: \.self) { label in
                    TextField(label, text: self.$text)
                        .textFieldStyle(RoundedBorderTextFieldStyle())
                }
            }
            .padding(.leading)
        }
        .padding(.horizontal)
        .fixedSize(horizontal: false, vertical: true)
    }
}

Here is the resulting preview:

in order to account for the misaligned baselines of the external and internal labels (a collateral issue that is not related to this specific layout – see for instance this discussion) I manually added the padding

credits to this website for enlightening me on the path to understanding
SwiftUI layout trickeries