Projects are not listed on the Public Portal by default. You can opt to list a project from the Project page, or quickly toggle this feature on from the Engagement Dashboard in the Active Projects list:
From your dashboard, scroll down to Active Projects, and in the Listed column, toggle the Listed on public portal toggle to off (white).
This works similarly for meetings, as well as archived projects.
This will remove the project from the Public Portal. To list a project, toggle the switch on (indicated in green.)