The MS style guide, which most C# code follows, says so.

https://learn.microsoft.com/en-us/dotnet/csharp/fundamentals/coding-style/identifier-names#pascal-case

I personally hate it and I prefer the java/js style. The braces are also horrible. Here’s an example.

public class ExampleEvents
{
    public bool IsValid;
    public IWorkerQueue WorkerQueue { get; init; }
    public event Action EventProcessing;
    public void StartEventProcessing()
    {
        static int CountQueueItems() => WorkerQueue.Count;
        // ...
    }
}