Ask HN: More open access online resource in higher education amid the pandemic?

Since the pandemic starts, most higher education has to be delivered online. As a result, lots of great online content must have been generated by awesome professors all over the world. Even better, some of them have decided to make it open to the public, for example, Terence Tao [announced](https://terrytao.wordpress.com/2020/03/14/course-announcement-math-247b-classical-fourier-analysis/) that his Math 247B will be available for everyone. So I am wondering if there is a trend of more openness for online higher education. Do you happen to encounter some awesome resources that you want to share? Also, what prevents the school/professor from releasing their content?