Why can't I view course materials after the professor added me as a guest to the course site?
Instructors can control whether or not the guest and observer roles have access to your course and to specific content. They must turn on access to each individual content item for guests.
Guests in a course can include guest lecturers, potential students, or other users who aren't directly participating in your course.
Observers are typically assigned to follow specific users in Blackboard Learn without interacting with the system. Observers can view your course and track student progress. Also, from a course, instructors can send email alerts to observers as needed.
After they log in, observers access information about their associated students on the Observer Dashboard accessed on the My Institution tab in the Tools panel.
For more information: https://help.blackboard.com/Learn/Instructor/Courses/Manage_Course_Enrollment/Guest_and_Observer_Access