A project has one of two visibility settings: public link, which allows anyone with the link to access the project, or private link, which requires an invitation in order to access the project.
By default, projects are set to private link.
To change project visibility, first access the project team screen. From a project page, click the project team icon in the top right navigation bar.
From the project team screen, click the text in the bottom left corner where the visibility is shown. From the menu, select the desired visibility setting.
These changes will be reflected when you close the project team menu and return to the project.