The same thing happened to me in .net core 3.1. In my case some server roles and features were missing

Checking the Application Event Log I found the error '0x8007023e'

Checking the System Event Log I found a WAS (Windows Process Activation Service) communication error:

Then I installed the following roles and features:

Also I reinstalled ASP.NET Core Module (is a native IIS module that plugs into the IIS pipeline, allowing ASP.NET Core applications to work with IIS)

Finally I had to reassign the app pool to the site, and everything worked (I'm using InProcess model)

ASP.NET Core 3.1 Runtime (v3.1.6) - Windows Hosting Bundle

You can download it from here.

I struggled a lot to find out this problem's solution . after 4 5 days research, I come to know the exact solution. Kindly follow all the below steps, definatly it will work for Nopcommerce 4.3 Issue using dotnetcore 3.1 or normal dotnetcore 3.1 project.

Step1 : check dotnet version and sdk using cmd

Step 2: add the IISUSER or you can also give Everyone permission to the main folder

Step 3: If it is nopcommerce 4.3 project then configure the path

and paste below folders in bin->debug->netcoreapp3.1

App_Data,Views,wwwroot,Plugins,Themes,logs,Areas/Views,web.config

Note : this is the main solution after adding the web.config under bin->debug->netcoreapp3.1

<aspNetCore processPath="C:\Program Files\dotnet\dotnet.exe" arguments=".\Nop.Web.dll" stdoutLogEnabled="false" stdoutLogFile=".\logs\stdout" forwardWindowsAuthToken="false" startupTimeLimit="3600" hostingModel="InProcess">

Note : If you have configured your site already in iis, then do the last step reset the iis using cmd. open cmd as administrator and run command iisreset

I hope this will resolve your all issues