One site that comes to mind is https://poetsandquants.com/ but it is career-focused mostly.
Another that used to be popular was is zH but the signal-noice ratio is terrible and it is too political.
There is a lot of finance talent here on HN, you should discuss and be pleasantly surprised.
It's about time someone consolidated and centralized (ironical, I know !) the knowledge in the industry.
1) https://quant.stackexchange.com/ forum is worth following
2) https://quantocracy.com/ for article aggregators but no support for comments
There's /biz/ which has some decent discussions from time to time, but being 4chan is also filled with trolls, shilling, and misinformation.
Seems like it's a good opportunity for someone inclined to create such a community.