Making a Course Visible in the new Moodle 3.5 version

Moodle's Course visibility setting determines whether the course appears in the list of courses and whether students can access it. If set to Hide, then access is restricted to users with the capability to view hidden courses (such as teachers).
This is useful for when you want to hide a course before the semester starts or after the semester ends.
 Often times this might be set to Hide without you even knowing, leading to confusion about a student's access to a course.
To check or modify your course visibility, please follow these steps.

To make your course visible:

• Login to Moodle.
• Click into the course that you wish to make visible to your students.
• On the right side of the screen, there is a gear icon that you must select. 

• Under the drop down menu that appears, you will select Edit settings.
• Once the Edit course settings menu appears, you will see the General settings. There you will find the Course visibility option. 

• Set the Course visibility to Show. This will now make your course visible to students.

For further details, please refer to this Making a Moodle Course Visible KBA.