@sharonyue I have noticed this as well. Which surprised me given the ubiquity of that icon in UI design these days. I could also say the same for the adaptive horizontal rule collapsable menu icon visible when in portrait or narrow windows. Yep. That icon IS also ubiquitous, especially smart phone side. But once again, while discoverable, not otherwise obvious. Go figure. Anyways, maybe a FAQ entry, maybe a "How To" or some "Getting Started" announcement. And/or accept the reality that no matter how easy you make it there are still those who're just not going to get it. Nor even try at it much.
As for highlighting the icon, I personally enjoy how generally understated NodeBB's UI is. Not a bunch of stuff competing for "click me" attention. It is very discoverable w/minimal effort. It's all there and. for the most part, stays out of my way. Yet.... I still have users "discovering things" several months after signing up. even among pretty active posters. Why? Because they're stupid? I think not. I suspect more a matter of habit. Folks are busy so they opt for lowest hanging fruit.
Speaking of UI design, one thing that maybe could be clearer is the two "Reply" buttons: one for the post itself and another for the thread. Both sporting the same label so that was source of minor confusion at launch. Communities are pretty good at teaching/sharing knowledge, however, so it did not take long for that one to percolate thru the new user base.
Sorry this is no help to your actual question and more of a "me too". I decided not to sweat it and let some responsibility remain with the user. Balance can be elusive.
P.S.; Not a dev but would seem this involves styling fa-ellipsis-v ?? Clue bats welcome.