Pretty much every language with a class that contains a function with a loop that breaks on an inner condition would be 4 levels deep. I suppose Objective-C would only be 3 deep, but I can't think of any others off the top of head.

I do like having the namespace there, if only to gently nudge you towards better architecture.

As a temp fix I have overridden Rider's code formatting to not indent within the namespace, but C# 10 will bring file scoped namespaces. You can just declare the namespace between the imports and the classes, and everything in the file will be namespaced automatically.