We have received feedback from one of customers when installed the nopCommerce. The following is the error message:

An error occurred while starting the application. .NET Core 4.6.26725.06 X64 v4.0.0.0 | Microsoft.AspNetCore.Hosting version 2.1.1-rtm-30846 |

When the error page is shown this means that there is some error and you need to know what the error is before fixing it. You have two options:

Open the administration by navigating to YourStoreName.com/admin and then go to System -> Log.
The Log contains all the errors and warnings in your store. Most of the time you should be looking for the most recent error. The error details contain all the information you need to investigate and fix the problem.

If you can't access the administration you have to turn on your site log, so that your errors are logged in a .txt file. To do so, modify your Web.config file by setting stdoutLogEnabled to true:

  <aspNetCore requestTimeout="00:07:00" processPath="%LAUNCHER_PATH%" arguments="%LAUNCHER_ARGS%" forwardWindowsAuthToken="false"
stdoutLogEnabled="false" stdoutLogFile=".\logs\stdout" />
change to:

  <aspNetCore requestTimeout="00:07:00" processPath="%LAUNCHER_PATH%" arguments="%LAUNCHER_ARGS%" forwardWindowsAuthToken="false"
stdoutLogEnabled="true" stdoutLogFile=".\logs\stdout" />

Once you got the error you will get a log .txt file generated in ~/Logs folder (~/Presentation/Nop.Web/Logs for Source version of nopCommerce). 

Hope it help! In case you are looking for reliable NopCommerce hosting, please kindly give us a look.