This video will show you how to create an ambient occlusion gradient post process effect in Unreal Engine, using Elias Wick - Blend Modes; now available on the Unreal Engine Marketplace, and Gumroad:
Elias Wick - Blend Modes
https://dev.epicgames.com/community/learning/tutorials/7Byn/unreal-engine-ambient-occlusion-gradient-effect-tutorial