TabViewCustomizationEnablerView.swift

import SwiftUI

struct ContentView: View {
    var body: some View {
        TabView { 
            Color.red
                .ignoresSafeArea()
                .tabItem { 
                    Label("Red", systemImage: "1.circle.fill")
                }
                .background { 
                    TabViewCustomizationEnablerView()
                }
            Color.orange
                .ignoresSafeArea()
                .tabItem { 
                    Label("Orange", systemImage: "2.circle.fill")
                }
            Color.yellow
                .ignoresSafeArea()
                .tabItem { 
                    Label("Yellow", systemImage: "3.circle.fill")
                }
                .ignoresSafeArea()
            Color.green
                .ignoresSafeArea()
                .tabItem { 
                    Label("Green", systemImage: "4.circle.fill")
                }
            Color.blue
                .ignoresSafeArea()
                .tabItem { 
                    Label("Blue", systemImage: "5.circle.fill")
                }
            Color.purple
                .ignoresSafeArea()
                .tabItem { 
                    Label("Purple", systemImage: "6.circle.fill")
                }
            Color.pink
                .ignoresSafeArea()
                .tabItem { 
                    Label("Pink", systemImage: "7.circle.fill")
                }
            Color.cyan
                .ignoresSafeArea()
                .tabItem { 
                    Label("Cyan", systemImage: "8.circle.fill")
                }
                .ignoresSafeArea()
            Color.gray
                .tabItem { 
                    Label("gray", systemImage: "9.circle.fill")
                }
        }
    }
}

fileprivate struct TabViewCustomizationEnablerView: UIViewControllerRepresentable {
    func makeUIViewController(context: Context) -> ViewController {
        .init()
    }
    
    func updateUIViewController(_ uiViewController: ViewController, context: Context) {
        
    }
    
    final class ViewController: UIViewController {
        override func didMove(toParent parent: UIViewController?) {
            super.didMove(toParent: parent)
            
            var _parent: UIViewController? = parent
            while let __parent: UIViewController = _parent {
                if let tabBarController: UITabBarController = __parent.tabBarController {
                    tabBarController.customizableViewControllers = tabBarController.viewControllers
                    break
                }
                
                _parent = __parent.parent
            }
        }
    }
}

#Preview {
    ContentView()
}