Supported Engine Versions: 4.25 - 4.27, 5.0

https://www.unrealengine.com/marketplace/en-US/product/simple-icon-creator

With Simple Icon Creator you can create icons directly in the engine. Run blueprint utility widget, modify: mesh settings, materials settings, light and then export your icon as 2D texture. You can create an icon with a transparent background. Icon is ready for use with UI.