Are instructors allowed to publish a course as an individual course plus include the same course in a larger course like a Masterclass course?

Yes, but this is subject to review. Any overlap in content across your courses must remain minimal.

Please keep in mind that courses are meant to help students learn within a safe environment. They are not meant to be used by instructors to market or sell to students in any way or form. If this happens, it results in students feeling distrustful because they’re being sold when they want to learn.