Startup.cs

using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.SpaServices;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;
using VueCliMiddleware;

namespace VueTemplate
{
    public class Startup
    {
        public Startup(IWebHostEnvironment env)
        {
            var builder = new ConfigurationBuilder()
                .SetBasePath(env.ContentRootPath)
                .AddJsonFile("appsettings.json", optional: false, reloadOnChange: true)
                .AddJsonFile($"appsettings.{env.EnvironmentName}.json", optional: true, reloadOnChange: true)
                .AddEnvironmentVariables();

            Configuration = builder.Build();
        }

        public IConfigurationRoot Configuration { get; }

        public void ConfigureServices(IServiceCollection services)
        {
            services.AddSpaStaticFiles(configuration => configuration.RootPath = "ClientApp/dist");

            services.AddControllersWithViews();

            services.AddLogging(opt =>
            {
                opt.AddConsole();
                opt.AddDebug();
                opt.AddConfiguration(Configuration.GetSection("Logging"));
            });
        }

        public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
        {
            bool success = int.TryParse(Configuration.GetSection("ClientAppPort").Value, out int port);

            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }
            else
            {
                app.UseExceptionHandler("/Main/Error");
                app.UseHsts();
            }

            app.UseStaticFiles();
            app.UseSpaStaticFiles();

            app.UseRouting();

            app.UseAuthorization();

            app.UseEndpoints(endpoints =>
            {
               endpoints.MapControllerRoute(
                    name: "default",
                    pattern: "{controller=Main}/{action=Index}/{id?}");

                if (System.Diagnostics.Debugger.IsAttached)
                {
                    endpoints.MapToVueCliProxy
                    (
                        "{*path}",
                        new SpaOptions { SourcePath = "ClientApp" },
                        npmScript: "serve",
                        regex: "Compiled successfully",
                        port: port,
                        forceKill: true
                    );
                }
            });
        }
    }
}