Discussion forums are one part of MOOCs that basically don't work at all. For technical courses that roll out on a schedule (which are probably not as common any longer), they're vaguely useful for platform issues and maybe some points of particularly common confusion. But they're swamped with people who are clearly way out of their depth, e.g. have no idea how to even begin to setup a required programming environment on their system.

From there, it descends into the absolute dumpster fire that is any sort of real discussion around less technical topics.