Demo showing a custom back button implemented using SwiftUI's NavigationStack

NavigationStack_CustomBackButton.swift

import SwiftUI

struct ContentView: View {
    
    @State private var path: [Fruit] = []
        
    var body: some View {
        NavigationStack(path: $path) {
            List {
                NavigationLink(Fruit.apple.name, value: Fruit.apple)
                NavigationLink(Fruit.orange.name, value: Fruit.orange)
                NavigationLink(Fruit.banana.name, value: Fruit.banana)
            }
            .navigationTitle("Fruits")
            .navigationDestination(for: Fruit.self) { fruit in
                FruitView(fruit: fruit) { nextFruit in
                    NavigationLink(value: nextFruit) {
                        Text("Next is \(nextFruit.name)")
                            .foregroundColor(.accentColor)
                    }
                    .buttonStyle(.plain)
                }
                .navigationBarBackButtonHidden()
                .toolbar {
                    ToolbarItem(placement: .navigationBarLeading) {
                        Button {
                            goBack()
                        } label: {
                            Image(systemName: "chevron.left")
                        }
                        
                    }
                }
            }
        }
    }

    func goBack() {
        _ = path.popLast()
    }
}

enum Fruit: String, Hashable, CaseIterable {
    case banana = "🍌"
    case orange = "🍊"
    case peach = "🍑"
    case apple = "🍎"
    
    static var random: Self {
        Self.allCases.randomElement()!
    }
    
    var color: Color {
        switch self {
        case .banana:
            return .yellow
        case .orange:
            return .orange
        case .peach:
            return .pink
        case .apple:
            return .red
        }
    }
    
    var name: String {
        switch self {
        case .banana:
            return "Banana"
        case .orange:
            return "Orange"
        case .peach:
            return "Peach"
        case .apple:
            return "Apple"
        }
    }
}
extension Fruit: Identifiable {
    var id: String { self.rawValue }
}

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}

struct FruitView<Link: View>: View {
    let fruit: Fruit
    var nextLink:  ((Fruit) -> Link)? = nil
    
    var body: some View {
        ZStack {
            fruit.color.opacity(0.2).ignoresSafeArea(.all)
            VStack {
                Text(fruit.rawValue)
                    .font(.system(size: 100))
                    .padding()
                nextLink?(Fruit.random)
            }
        }
        .navigationTitle("\(fruit.name)")
    }
}