The shaders allow turning an unfinished scene into eye-catching graphics. Setting up shaders properly helps achieve beautiful, clean colors, and a stylized cartoonish look.
Black shadows are what you should be avoiding. Cartoon-looking shaders make the scene look more casual-genre. This type of shadow also makes working with this setting a lot easier.
The key principle is again setting up a limitation. As a rule, there is a side of the object that is lit and a shadowy side. Both sides contain one color in all places and no halftones.
The shadows shouldn't be too dark or seem dirty. This feeling is created when black and gray colors are used, so it is better to make the shadows colored — blue, green, or purple. Unity
Asset Store offers a variety of shaders that are free and simple to work with, For example, here is the Flexible Cel Shader