What is the necessary entity that cannot be done by professor without physical classroom with assembled students? I want to know whether there is any necessary entity (quality/property) in the traditional classroom teaching that cannot be done without a physical classroom with intended students. Please keep aside the administrative responsibilities such as minimum teaching hours in classroom, availability in office, maintaining attendance of students etc.,

Afaik, most of the tasks that a professor (any lecturer) can do in the classroom can also be done without classroom with assembled students, nowadays, with high availability.

For lecture, a professor can publish her recorded video lectures to students. For query solving or interaction, she can use the Q&amp;A site for her students. Announcements can also be streamed in a similar way. I'm referring to the sites such as Google classroom, piazza, slack, etc.,

In such a case, I'm getting the doubt whether there exists a necessary entity that a professor cannot provide without (her direct presence) a classroom teaching.

If such an entity exists, then what is that?
Have you ever taught? When you explain something to a class, have you ever seen understanding happen in students' faces, or confusion? When the former happens, have you stopped your speaking and prompted the student to continue your thought and make it their own? Or in the latter case, have you stopped and asked what was unclear, had a discussion about it, and then tried to explain it in a different way?

None of this happens in an online setting: You give students a textbook chapter to read or a video to watch, but it's not interactive: You can't catch students where they need to be caught to learn efficiently because you don't have the personal interaction and contact. Personal contact really is a very powerful thing.