there’s a tutorial called “Polyphony” in the reference that should explain the poly~ object in full. you basically need to add outlets in order for them to show up.
the problem you’re having is that you’re looking at another monome app and it’s just a blank box right ? you must be missing the dependency for some reason
go to File > Show Package Manager. in the package manager you’ll see the monome package - install that. at this point if you restart max it may show up, if not just type bpatcher serialosc, and you’ll get a working object, which you can switch out with the blank box.