In eevee, the soft shadows of the sun have circular pattern artifacts The angle value has been increased to get soft shadows with sun.
As the rendering progresses, the shadows appear to spread smoothly, but soon there are circular pattern artifacts.
This looks like a step phenomenon or constant interpolation.
I tried to manipulate all the values of the light and render properties, but couldn’t improve the artifacts.
How can I improve this problem?
I’ve attached two blend files that I set up to help you solve my problem.
Work was done in blender 2.81.  

file01
file02
I think you're just seeing the difference in shadow rendering quality between preview and final render.  If I load your scene, the preview looks similar to the above:



but a true F12-initiated render looks far better: