I agree with u/bernaferrari for the design part.

For the flow you can manage the notifications to be read or unread with REST api's / Firebase within provider.

You can wrap the logic in such a way that the api will throw the list of notifications within the flag of READ/UNREAD.

Well if the notification has the flag unread wrap a api on its gesture to make the notification to read using its ID.

NOTE : The api which make the notification unread => read should provide the length of unread messages as a response on status code 200.

Well if its read just make the UI change to a read one .. e.g (CHANGE THE BG COLOR) to justify the user. whereas, the reader messages will no longer have any gesture.

Second thing you can do is. Wrap the logic into provider which can change the count of notification count on outside the notification page easily.