When an Opportunity is Won, a Project is created. New Projects do not have any Project Tasks. You will need to add the Tasks as part of Project Planning.
This article explains how to apply a Task Template to a Project. To see how to add Tasks directly to a Project, see Project Tasks.
Check out this article to learn the benefits of using Task Templates for Project Planning.
Apply Task Template to a New Project
Go to the Tasks view in a Project, click the Ellipsis menu (three-dot menu), and click Apply task template. This will open a modal to select the Template. Select the Template and click “Apply.”
You will see that all the Task Groups, Tasks, and Checklists from the Template are now available in the Project. Proceed to reviewing the Task List and adding or removing Tasks, adding more details to the Tasks, and scheduling the Tasks.
Learn more about scheduling Project Tasks
Apply Task Template to an Ongoing Project
Task Templates can also be applied to an ongoing project with Tasks already added. Note that applying a Task Template will delete all existing Tasks in the Project. So, you will lose the Schedule and Time Tracks relevant to the Tasks.
This is also the expected behavior when you change Task Templates for a Project. The Groups, Tasks, and Schedule of the existing Template are deleted.