Why the sun is so ugly in 5.8?

Why the sun disk is so ugly in the U5.8 even with high settings? Im new to unreal, but the does not math with the other features.

So, simply you have to write your material. But, it is easy to plug custom hlsl on custom nodes. https://youtube.com/shorts/akCq8wjJd2A?is=p2CqMoVGRnKKW4A3