Restrict access
From MoodleDocs
The restrict access feature enables teachers to restrict the availability of any activity or even a course section according to certain conditions such as dates, grade obtained, group or activity completion.
Restrict access is enabled by default in new installations of Moodle 3.1 onwards.
Note: If you don't see a 'Restrict access' option when setting up course activities and sections, check with the administrator that it is enabled in Site administration > Advanced features.