This question already has an answer here:
Each site used to have its own chat room(s), even beta sites.
Is it a new policy, or a bug, or my fault?
See the URL in the lower left when I hover my mouse on "chat":
When I click on it, it sends me to a page where 27 pages of chatrooms appear, with entertaining names such as "Maid Café" or "The Frying Pan", and finding which ones are about information security is a big challenge.