If you want to clean up your sidebar or get rid of that annoying Topic that isn't relevant to your interests anymore, follow the steps below.
Click the [Discover Topics] button on the right sidebar.
There, you can unfollow a Topic by clicking the [check] button in the upper right corner of any Topic.
Another way to unfollow a Topic is to view the Topic you would like to unfollow. On the bottom right corner of the banner, hover over [Following] which then gives you the unfollow option, click the [Unfollow] button.
*If the option is not available to unfollow — or if the checkmark is greyed out — then your organizational admin has not given the permission to unfollow.