ContentView.swift

struct ContentView: View {
    @State var atTop = true
    @Namespace var ns

    var body: some View {
        VStack {
            VStack {
                Text("Top")
                    .border(.green)
                    .opacity(atTop ? 1 : 0)
                    .matchedGeometryEffect(id: "text", in: ns, properties: .position, isSource: atTop ? true : false)

                Spacer()

                Text("Bottom")
                    .border(.blue)
                    .opacity(atTop ? 0 : 1)
                    .matchedGeometryEffect(id: "text", in: ns, properties: .position, isSource: atTop ? false : true)
            }
            .frame(width: 64)
            .frame(maxHeight: .infinity)
            .border(.red)

            Button("Move") {
                withAnimation(.default) {
                    atTop = !atTop
                }
            }
        }
        .padding()
    }
}