Using Environment variable in program.cs in Angular

I am trying to use a custom exception handler and include it in the program.cs

it is giving me error that the env variable is a string. How to do that? How to make the env variable available to be used in the function?

var app = builder.Build();
var env = Environment.GetEnvironmentVariable("ASPNETCORE_ENVIRONMENT");
app.ConfigureExceptionHandler(env);

as the ConfigureExceptionHandler is the exception file:

using System.Net;
using Microsoft.AspNetCore.Diagnostics;

namespace API.Extensions
{
public static class ExceptionMiddleWareExtentions
{
    public static void ConfigureExceptionHandler(this IApplicationBuilder app, IWebHostEnvironment env)
    {
         if (env.IsDevelopment())
        {
            app.UseDeveloperExceptionPage();
        }
        else
        {
            app.UseExceptionHandler(
                options => {
                    options.Run(
                        async context =>
                        {
                            context.Response.StatusCode = (int)HttpStatusCode.InternalServerError;
                            var ex = context.Features.Get<IExceptionHandlerFeature>();
                            if(ex != null)
                            {
                                await context.Response.WriteAsync(ex.Error.Message);
                            }
                        }
                    );
            });
        }
    }
}