You can use the presentationMode var from the environment inside a Button:
See the commented example below for a possible implementation.

struct ContentView: View{
    
    var body: some View{
        // I am navigating with a Navigationlink, so there is
        // no need for it in the AnadirDatosViewA
        NavigationView {
            NavigationLink("show AnadirDatosViewA") {
                AnadirDatosViewA()
            }
        }
    }
}

struct AnadirDatosViewA: View {
    @Environment(\.presentationMode) var presentation
    
    var body: some View{
        // if you navigated to this by a Navigationlink remove the NavigationView
        Color(red: 48 / 255, green: 49 / 255, blue: 54 / 255)
            .edgesIgnoringSafeArea(.all)
            .overlay(
                HStack{
                    // This Button will dismiss the View
                    Button("Back"){
                        // with help of th presentationMode from the environment
                        presentation.wrappedValue.dismiss()
                    }
                    // This NavigationLink can forward you to another view
                    NavigationLink("Next") {
                        TextView(text: "last")
                    }
                }
                // This will hide the back Button in this View
            ).navigationBarBackButtonHidden(true)
    }
}
// HelperView
struct TextView: View{
    var text: String
    var body: some View{
        Text(text)
    }
}