They say something about posting 3 times a week. Even if it’s not a formal obligation, it’ll certainly feel like one if they notice you never post whilst other people do.
it's pretty interesting to see this discrepancy in response to this idea
some folks -- i guess like you? -- read this and think, "oh, great. a mandate that fixes a problem i don't have, and now might be something i'm forced to participate in against my will"
and other folks -- definitely me, and i believe the OP as well -- read this and think, "oh, great! an idea that might help me with a problem that i have, and might be something i can point-to as one possible solution to that problem"
The difference is for me, that problem is already solved naturally. If you have the right work environment and culture, you’ll already have a bunch of fun and interesting work chats going on. If you need to force it, something else is wrong.