Pass the input as the first argument. You can pass schemes (`ms-calculator://whatever`) or files (`C:/windows/system32/calc.exe).

no-arguments-rce.cs

using System;
using System.Diagnostics;
using System.Runtime.InteropServices;

namespace runme
{
    class Program
    {
        static void Main(string[] args)
        {
            string nem = args[0];
            OpenFileOrUrl(new Uri(nem).ToString());
        }

        public static void OpenFileOrUrl(string pathOrUri)
        {
            if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
            {
                try
                {
                    // Is the scheme not http or https?
                    if (!IsPathForBrowser(pathOrUri))
                    {
                        Console.WriteLine(String.Format("Executing: Process.Start({0});", pathOrUri));
                        Process.Start(pathOrUri);
                        return;
                    }
                }
                catch (Exception exception)
                {
                    Console.WriteLine("Error in Process.Start");
                    Console.WriteLine(exception.ToString());
                }
                pathOrUri = "\"" + pathOrUri + "\"";
                Console.WriteLine(String.Format("Executing: explorer.exe {0}", pathOrUri));
                Process.Start("explorer.exe", pathOrUri);
                return;
            }
            Process.Start("open", pathOrUri);
        }

        private static bool IsPathForBrowser(string path)
        {
            return Uri.IsWellFormedUriString(path, UriKind.Absolute) && IsUriForBrowser(new Uri(path));
        }

        private static bool IsUriForBrowser(Uri uri)
        {
            return (uri.Scheme == Uri.UriSchemeHttp) || (uri.Scheme == Uri.UriSchemeHttps);
        }
    }
}