The old UILocalNotification class in UIKit was deprecated back in iOS 10, and has now been replaced with a new framework called UNNotificationRequest.
I've created a Feedback case to request this gets implemented in Xojo iOS. Notifications are a pretty important part of most mobile apps. It's unclear when Apple will pull the plug on UILocalNotification but they could do it any time.
If you'd like Xojo to handle Notifications in your mobile apps, please give this case some points.
Out of interest, has anyone explored implementing UNNotificationRequest in Declares yet?