Thanks Marc for your answer.
That's too bad. I really wish the Notifications could keep track of what you've visited and what you haven't, like on an email program for example. When I have multiple notifications and open the menu, and click one notification to visit the post, maybe type an answer, and then come back to the notification menu, I can no longer tell which notifications I've already clicked and which I haven't.
Let's call it a feature request for a future version of the software! 😃