In My Courses, we can see the completion percentage of each course we are enrolled in. How do we add this option if it is not visible?

This option can be controlled from administration. If it is not active by default, you can edit your courses to configure each one to display it. To do this, access the course settings by editing your course, clicking on the gear icon, and selecting Course Administration > Settings.

On the settings page, open Completion tracking and select Yes. Remember to Save.