Basically, I need to do the same thing as [this answer](https://tex.stackexchange.com/q/85479/129388) but with overleaf instead. I tried the following. I  opened two windows of the same project. I placed each one of them on a different monitor. In one I let the code go fullscreen, while in the other one I let the pdf preview go full screen. 
But the pdf preview doesn't get updated even if the code on one screen gets compiled? I have to separately compile the pdf window too.