possibility to auto delete notification via the x button on popup.

[rexxDZN]

This is something Microsoft itself isn't fixing, and it is so annoying, making the notification center not useful for productivity since it gets cluttered. I don't understand the design: how they use the same button (x) twice and if it does different things. On the center, it completely removes it, and on the popup, it simply dismisses it—which is unnecessary extra behavior.

[SamsidParty]

This would be a great feature, however Microsoft does not expose any interface for dismissing or checking dismissal of notifications. Further reverse engineering would be required to implement this, which will take a long time.