Visual Effect "Light" of Greasepencil doesn't exist I have seen lighting effects being used in a 2019 Greasepencil tutorial, but it is not listed in the Visual Effects tab. Is it removed from Blender?
Greasepencil's draw-engine was refactored and now GP objects can interact with 3d lights, so the light effect was removed. See point 1.3 in this post.