This is a paid asset, but now you can download UI Advanced Mask for FREE, but please remember this package is provided only for learning purposes or to be able to test before buying the product, NOT FOR COMMERCIAL PURPOSES.
Detail this asset from Unity Store: Original Link
UI Advanced Mask v1.12
UI Advanced Mask is a plugin highly focused on UI masking. It’s designed to work with unity native uGUI system, but also able to work in 3d game world. Unity natively includes a UI mask feature, but it’s not perfect. It’s using cutoff and can’t have smooth edge or half transparent. Therefore i develop this ortho-projector-like UI mask plugin with ui pointer raycasting, so that we can do beautiful masking on 2D/3D UI. All position/scale/rotation/size is based on RectTransform even if it’s not in a canvas.