I bought a benq gw2470ml 2 days ago and had plugged it in to my laptop through HDMI port, everything runs perfectly, except when I try to run a game IE (Overwatch). My laptop can run Overwatch without the monitor and Epic settings and get over 100fps, but as soon as I make my monitor the main display for the game is gets like 20fps and its super choppy. I have no idea why and there's absolutely nothing on the internet about how to fix this.
What make/model laptop do you have? It sounds like its using integrated graphics out of that port (monitor doesn’t have anything to do with FPS unless V-Sync is on, and then it would be limited to the refresh rate of 60Hz)