A few people have reported poor mouse performance in menus, etc, sometimes also associated with in-game stuttering. Unfortunately I don't think there is just an option you can check off to fix it, but people have had some success getting rid of the problem.

With FoV installed (or with DKS, a remastered version of D2:ED with the add-on) there is a 30 FPS limit, imposed to fix this mouse and stuttering problem some people had. There was an issue allowing the cap to be disabled, which Larian is in the process of tracking down, so for now even people who had no trouble are limited to 30 FPS.
I'm not advocating getting the add-on just to fix this problem, though, or guaranteeing that would help.


Mouse is very sloppy, any fixes?

Game is stuttering, also the cursor in the menu


First Aid Kit for Divinity II

First Aid : when Div2 does not start or crashes


Choppy game - possible fix

For people with stuttering graphics