Example of how you can create a Master Detail data editing and creation flow in SwiftUI.

MasterDetailEdit.swift

//
//  BindingTest.swift
//  MutatingState
//
//  Created by Michael Nino Evensen on 21/12/2022.
//

import SwiftUI

struct Object: Identifiable {
    var id = UUID()
    var value: Int
    var string: String?
    var date: Date?
    
    init(value: Int = 1, string: String? = nil, date: Date? = nil) {
        self.value = value
        self.string = string
        self.date = date
    }
    
    struct MutableData {
        var value: Int = 1
        var string: String = ""
        var date: Date = .now
    }
    
    var mutableData: MutableData {
        return MutableData(value: value, string: string ?? "", date: date ?? .now)
    }
    
    mutating func update(with data: MutableData) -> Self {
        self.value = data.value
        self.string = data.string
        self.date = data.date
        return self
    }
}

struct BindingTest: View {
    @State private var showNewItemSheet: Bool = false
    @State private var items = [Object]()
    
    // New
    @State var new = Object()
    
    var body: some View {
        NavigationStack {
            List($items) { item in
                NavigationLink {
                    BindingTestDetailView(initialValue: item)
                } label: {
                    HStack {
                        VStack(alignment: .leading) {
                            if let title = item.wrappedValue.string {
                                Text(title)
                            }
                            if let date = item.wrappedValue.date {
                                Text(date.formatted(.dateTime.day().month()))
                                    .foregroundColor(.secondary)
                                    .font(.caption2)
                            }
                        }
                        Spacer()
                        Text(String(describing: item.wrappedValue.value.formatted(.number)))
                            .foregroundColor(.secondary)
                        
                    }
                }

            }
        }
        .safeAreaInset(edge: .bottom) {
            Button("+ Add new") {
                showNewItemSheet = true
            }
            .buttonStyle(.borderedProminent)
        }
        .sheet(isPresented: $showNewItemSheet) {
            BindingTestDetailView(initialValue: $new, didSave: { newItem in
                self.items.append(newItem)
                
                // Reset
                new = Object()
            })
        }
    }
}

struct BindingTestDetailView: View {
    @Environment(\.dismiss) private var dismiss
    @Binding var obj: Object
    @State private var didSpecifyDate: Bool = false
    
    // Mutable local state
    @State private var mutable = Object.MutableData()
    let didSave: ((Object) -> Void)?
    
    init(
        initialValue: Binding<Object>,
        didSave: ((Object) -> Void)? = { _ in }
    ) {
        self._obj = initialValue
        self.didSave = didSave
        self._mutable = State(initialValue: initialValue.wrappedValue.mutableData)
        if let _ = initialValue.wrappedValue.date {
            self._didSpecifyDate = State(initialValue: true)
        }
    }
    
    var body: some View {
        VStack {
            Text(String(describing: self.mutable))
            
            TextField("String", text: $mutable.string)
            
            Toggle(isOn: $didSpecifyDate) {
                Label("Has Date", systemImage: "calendar")
            }
            
            if didSpecifyDate {
                DatePicker("Date", selection: $mutable.date, displayedComponents: .date)
            }
            
            Stepper(mutable.value.formatted(.number), value: $mutable.value, in: 0...10)
            
            Button("Save") { save() }
                .buttonStyle(.borderedProminent)
        }
        .padding()
    }
    
    private func save() {
        var updated = self.obj.update(with: mutable)
        
        // Remove date if unspecified
        if didSpecifyDate == false {
            self.obj.date = nil
            updated.date = nil
        }
        didSave?(updated)
        dismiss()
    }
}

struct BindingTest_Previews: PreviewProvider {
    static var previews: some View {
        BindingTest()
    }
}