As you complete project tasks, you can bring them up and mouse over the Active button. It will then change to Archive as you hover over it. When you click the button, the task will be archived. This method will remove the task from the project entirely and hide it from view.
If you ever need to see tasks that have been archived, there is a search view already created for Archived that you can apply to your searches. Alternatively you can use the advanced filter skills you will learn in Chapter 10, Creating Advanced Searches and Dashboards to set a filter that displays records in which active records are false.
Previously in Odoo, a Done status was provided by default. If you need to keep track of completed tasks and not have them fall off the project, you will need to set up a Done or Completed stage for your project.