Two instances of the app exist after resuming killed app from Notification

I have the following project in Github where I used the Navigation component in it: https://github.com/alirezaeiii/Compose-Sample

In the Detail screen, I have a deepLink button that creates a pending intent and a notification :

val pendingIntent = findNavController()
                    .createDeepLink()
                    .setDestination(R.id.detailFragment)
                    .setArguments(args.toBundle())
                    .createPendingIntent()
                Notifier.postNotification(args.poster, requireContext(), pendingIntent)

Here is how I generate the notification :

fun postNotification(poster: Poster, context: Context, intent: PendingIntent) {
        val summary = NotificationCompat.Builder(context, channelId)
            .setContentTitle(poster.name)
            .setContentText(poster.release)
            .setAutoCancel(true)
            .setContentIntent(intent)
            .setSmallIcon(R.drawable.donut_with_sprinkles)
            .setGroup(poster.id.toString())
            .setGroupSummary(true)
            .build()

        val notification = NotificationCompat.Builder(context, channelId)
            .setContentTitle(poster.name)
            .setContentText(poster.release)
            .setAutoCancel(true)
            .setContentIntent(intent)
            .setSmallIcon(R.drawable.donut_with_sprinkles)
            .setPriority(NotificationCompat.PRIORITY_HIGH)
            .setGroup(poster.id.toString())
            .build()

        val notificationManager = NotificationManagerCompat.from(context)
        notificationManager.apply {
            notify(
                "summary ${poster.id}",
                0,
                summary
            )
            notify(
                "notification ${UUID.randomUUID()}",
                0,
                notification
            )
        }
    }

When I generate multiple notifications, and then kill the app and resume the detail screen from notification items and exit the app, I start the app from the launcher icon, it seems two instances of the app exist since I need to click multiple times on the back button to exit the app. How can I resolve it?

Addenda

One working solution that I found for it was to add singleTop as launch mode to Activity instead of default one which is standard :

android:launchMode="singleTop"