You can write and on the screen of Surface Laptop but it's going to wobble. Putting a hand behind the screen may provide some support, but the experience is not very different from drawing on a hard back pad while standing. The drawing and writing performance is similar to that on the Surface Pro 2017.
I'll be putting out two more videos regarding the Surface Laptop. One will be the detailed review. The other will be a comparison review against the Surface Pro 2017. Be sure to subscribe to my Youtube channel to look out for them.