I'm unclear on what read-only status means when a course ends. I've been experimenting, and it appears that after a course passes the end date with "Users can only participate in the course between these dates" checked, students are unable to take quizzes but are allowed to post to graded and other discussions, and submit file assignments. With a quiz, the message "This quiz is no longer available as the course has been concluded" appears. If the course is concluded, and read-only, why are some posting activities still allowed?
The course end date is set in Course details.
The section end date is also set, and later than the course end date. How do these two dates interact? Could it allow certain activities but not others?