For example: If i wanted to attach point light to a mouse cursor (Witch is not possible i know) I want the light to follow ur mouse cursor while in a screen gui. I already made a custom mouse cursor that glows to give it more of a light effect but not sure if it's even possible to add light to a mouse cursor.
If you want to change the mouse image, you can use https://developer.roblox.com/en-us/api-reference/property/Mouse/Icon
If that is not what you're looking for; since it's a ScreenGui, do you want to get a sort of image label that represents a glow and follows the mouse?
I think this wiki from the developers page shows an example of that: https://developer.roblox.com/en-us/api-reference/function/UserInputService/GetMouseLocation