Visual Studio 2019 unhandled exception for all projects - unable to debug

I’m getting this error message when trying to debug projects (ANY!)

“An unhandled exception of type ‘System.IO.FileNotFoundException’ occurred in Unknown Module.
Could not load file or assembly ‘System.Runtime, Version=4.2.2.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a’ or one of its dependencies.
The system cannot find the file specified.”

I have been building a .NET Core Web project (MVC) in VS 2019 (Enterprise) ver. 16.6.30309.148 on Windows 10 (ver 2004 OS Build 19041.388)
3 days ago I started getting the above error and the project would not compile in VC.

However, the solution works absolutely fine being built from command prompt or in VS Code.

Tried building a completely new solution from VC templates and it shows the same error yet runs in VSCode. I am also unable to debug any older projects that work (and have previously worked) fine in VS Code.

I have tried uninstalling VS and installing it again, tried repairing it from msi, checked permissions to temp files, updated packages as suggested in similar posts. But here I am days later still trying to figure out how to make this work.

This happens even for a completely clean template project created with VS. (New > ASP.NET Core Web Application > MVC

[EDIT!!!] Updated VS to 16.6.5 (today’s release) and my projects run again.
Anyways the issues were coming up with the below template …

SDKs:
.NET Core SDK (reflecting any global.json):
Version: 3.1.302
Commit: 41faccf259

Runtime Environment:
OS Name: Windows
OS Version: 10.0.19041
OS Platform: Windows
RID: win10-x64
Base Path: C:Program Filesdotnetsdk3.1.302

Host (useful for support):
Version: 3.1.6
Commit: 3acd9b0cd1

.NET Core SDKs installed:
3.1.201 [C:Program Filesdotnetsdk]
3.1.302 [C:Program Filesdotnetsdk]

.NET Core runtimes installed:
Microsoft.AspNetCore.All 2.1.20 [C:ProgramFilesdotnetsharedMicrosoft.AspNetCore.All]
Microsoft.AspNetCore.App 2.1.20 [C:ProgramFilesdotnetsharedMicrosoft.AspNetCore.App]
Microsoft.AspNetCore.App 3.1.3 [C:ProgramFilesdotnetsharedMicrosoft.AspNetCore.App]
Microsoft.AspNetCore.App 3.1.6 [C:ProgramFilesdotnetsharedMicrosoft.AspNetCore.App]
Microsoft.NETCore.App 2.1.20 [C:Program FilesdotnetsharedMicrosoft.NETCore.App]
Microsoft.NETCore.App 3.1.3 [C:ProgramFilesdotnetsharedMicrosoft.NETCore.App]
Microsoft.NETCore.App 3.1.6 [C:ProgramFilesdotnetsharedMicrosoft.NETCore.App]
Microsoft.WindowsDesktop.App 3.1.3 [C:ProgramFilesdotnetsharedMicrosoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 3.1.6 [C:ProgramFilesdotnetsharedMicrosoft.WindowsDesktop.App]

*.csproj

<Project Sdk="Microsoft.NET.Sdk.Web">

  <PropertyGroup>
    <TargetFramework>netcoreapp3.1</TargetFramework>
  </PropertyGroup>

</Project>

startup

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.HttpsPolicy;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;

namespace App
{
    public class Startup
    {
        public Startup(IConfiguration configuration)
        {
            Configuration = configuration;
        }

        public IConfiguration Configuration { get; }

        // This method gets called by the runtime. Use this method to add services to the container.
        public void ConfigureServices(IServiceCollection services)
        {
            services.AddControllersWithViews();
        }

        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }
            else
            {
                app.UseExceptionHandler("/Home/Error");
                // The default HSTS value is 30 days. You may want to change this for production scenarios, see https://aka.ms/aspnetcore-hsts.
                app.UseHsts();
            }
            app.UseHttpsRedirection();
            app.UseStaticFiles();

            app.UseRouting();

            app.UseAuthorization();

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

Program.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;

namespace App
{
    public class Program
    {
        public static void Main(string[] args)
        {
            CreateHostBuilder(args).Build().Run();
        }

        public static IHostBuilder CreateHostBuilder(string[] args) =>
            Host.CreateDefaultBuilder(args)
                .ConfigureWebHostDefaults(webBuilder =>
                {
                    webBuilder.UseStartup<Startup>();
                });
    }
}

launchSettings.json

{
  "iisSettings": {
    "windowsAuthentication": false,
    "anonymousAuthentication": true,
    "iisExpress": {
      "applicationUrl": "http://localhost:50221",
      "sslPort": 44395
    }
  },
  "profiles": {
    "IIS Express": {
      "commandName": "IISExpress",
      "launchBrowser": true,
      "environmentVariables": {
        "ASPNETCORE_ENVIRONMENT": "Development"
      }
    },
    "App": {
      "commandName": "Project",
      "launchBrowser": true,
      "applicationUrl": "https://localhost:5001;http://localhost:5000",
      "environmentVariables": {
        "ASPNETCORE_ENVIRONMENT": "Development"
      }
    }
  }
}