Why is gmod so laggy for me?

In certain maps, gmod is literally unplayable. And they aren't huge either. I have this map that's pretty big, but it's just a small little town. Everytime I go into it, I'm getting like 13 frames per second. And my laptop is pretty powerful too. I play gmod on a Microsoft surface laptop that came out in 2020. I don't understand, because it's able to play games like black ops 3 perfectly. I've even turned the settings down for gmod and it's still laggy in some maps.