Long answer: In the United States, many colleges and universities use educational CMS platforms such as Canvas and Piazza for sharing course content with enrolled students. I used Canvas as a UC Santa Cruz grad student, San Jose State University part-time lecturer, and now as a tenure-track instructor at Ohlone College (a two-year community college). This was not the case when I was an undergrad at Cal Poly 20 years ago; CS professors placed their course content on their personal websites, and non-CS professors handed out their syllabi and other course assignments on paper.

The consequence of the use of platforms like Canvas is that course materials are usually not available to students not enrolled in the course. Granted, this is the same situation as in the pre-CMS days when most professors handed out course information by paper. However, it makes it harder for non-enrolled students to see what the classes are like.

Your best bet would be to take advantage of MIT’s Open Courseware, which contains the syllabi, lecture notes, problem sets, and exams for many MIT courses in a variety of subjects.

Also, there are some courses that have become famous, such as Harvard’s MATH 55 and Stanford’s CS 229. It should be possible to find the course materials, except for exams, for these courses.