Based on your question, it depends on your application structure.
For the first part, sales man target achievement notification, is related to their goals that they have achieved, I assumed that it must be sent from server side so you need push notification, but if user works with your App everyday you can submit next day notification locally using pull notification.
Also for the second approach you need push notification, it`s not as hard as it seems, based on your question category, you are using Xamarin, so it`s easy to implement using Xamarin.Firebase (Nuget package) try to send Push notification from your Server to your clients based on their ID or Topic Subscription.
Firebase Cloud Messaging - Xamarin | Microsoft Learn[
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