If you have posts in your "whats New" list, and you dont want to read them all to clear your unread post icon, then there is a simple way to clear your unread items.
In desktop view, when you have clicked on the whats new tab, you can click the button shown below.

In mobile view, you would click on the little menu icon, select the forums tab and then "Mark Forums Read" as in the image below.

Thats it!
In desktop view, when you have clicked on the whats new tab, you can click the button shown below.

In mobile view, you would click on the little menu icon, select the forums tab and then "Mark Forums Read" as in the image below.

Thats it!