That's what was good about the early stages of sites like Coursera, Udacity and Edx - they had quizzes, exercises and exams that are auto-graded that provided that kind of valuable feedback for all tiers.

I think they've all evolved now to where that is only available for paid tiers.

One innovation I really enjoyed was marking and commenting another student's answers, once you'd submitted your own. There are flaws but it's a valuable variation on graded feedback.