AppDelegate.swift

import UIKit
import PluggableApplicationDelegate

@UIApplicationMain
class AppDelegate: PluggableApplicationDelegate 
{
    override var services: [ApplicationService] {
        return [
            LoggerApplicationService()
        ]
    }
}

LoggerApplicationService.swift

import Foundation
import PluggableApplicationDelegate

final class LoggerApplicationService: NSObject, ApplicationService 
{
    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey : Any]? = nil) -> Bool {
        print("It has started!")
        return true
    }
    func applicationDidEnterBackground(_ application: UIApplication) {
        print("It has entered background")
    }
}

PluggableApplicationDelegate.swift

public protocol ApplicationService: UIApplicationDelegate {}

open class PluggableApplicationDelegate: UIResponder, UIApplicationDelegate 
{
    public var window: UIWindow?
    
    open var service  s: [ApplicationService] { return [] }
    private lazy var __services: [ApplicationService]! = {
        return self.services
    }()
    
    @available(iOS 3.0, *)
    public func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey : Any]? = nil) -> Bool {
        return !__services.contains(where: { service in
            return (service.application?(application, didFinishLaunchingWithOptions: launchOptions) ?? false) == false
        })
    }
}

See the full PluggableApplicationDelegate: https://github.com/fmo91/PluggableApplicationDelegate/blob/master/PluggableApplicationDelegate/Classes/ApplicationServicesManager.swift