ConfigurationManager was added to support ASP.NET Core’s new WebApplication model, used for simplifying the ASP.NET Core startup code. 
However ConfigurationManager is very much an implementation detail. It was introduced to optimise a specific scenario (which I’ll describe shortly), but for the most part, you don’t need to (and won’t) know you’re using it.
In this post, We take a look at the ConfigurationManager class, why it was added, and some of the code used to implement it.
[ Article ] : Looking inside ConfigurationManager in .NET 6: Exploring .NET 6 - Part 1