question

com.urbanairship.accengage.PackageUpdatedReceiver: Targeting S+ (version 31 and above) requires that an explicit value for android:exported be defined when intent filters are present]

Based on this error, you should add android:exported to PackageUpdatedReceiver not add it to MainActivity. If PackageUpdatedReceiver is a broadcast receiver, you can add android:exported property like following code.

[BroadcastReceiver(Enabled = true, Exported = true)]
    public class PackageUpdatedReceiver : BroadcastReceiver
    {
        public override void OnReceive(Context context, Intent intent)
        {
            Toast.MakeText(context, "Received intent!", ToastLength.Short).Show();
        }
    }

I donot know if you used statically-registered broadcast receiver or include intent-filters. You can refer this thread about setting true or false for Exported

For a statically-registered broadcast receiver, the Enabled properly must be set to true, otherwise Android will not be able to create an instance of the receiver.

For dynamic-registered broadcast receiver. The Exported property controls whether the broadcast receiver can receive messages from outside the application. If there is at least one intent-filter for the broadcast receiver the Exported property is true. If there are no intent-filters associated with the broadcast receiver, this value could be false.