Meta: I have had the same question as well and I'm sure that I will have it again in six months. IMO this submission has potential to be a regularly re-submitted post like 'Who is hiring?'.
Most of the replies here are more suitable to "what are good moocs", which is fine and what I more or less expected anyway.
As to regularly resubmitted post, this kind of touches the issues I asked. If there aren't many (or none) good new materials then there is no much point reposting same things again and again, similar threads from 2016 or 2018 will do. Some communities post a compilation of what new courses are gonna start soon. I don't find these useful, because they end up being just a huge dump of everything. I guess what I would find interesting is a recurring post about learning that goes like like "what are you learning/learnt recently/this year/this season" and why a mentioned source of learning was good. This naturally will focus on quality rather than quantity.