I post and comment here for discussion. I read reddit when it comes up in a google search about things ENWorld covers, and occasionally peruse some of the subreddits for games ENWorld doesn't have a large audience for. For example I'm running a Masks: The New Generation RPG which is PbtA. But even in those cases I'm likely not posting, just consuming and occasionally replying.
Just for completeness, I give answers and critiques on several Facebook D&D groups, but there doesn't seem to a method of discussion there besides arguing. I don't initiate posts there either.