The newest version of NopCommerce (4.x) requires ASP Core 2, not .NET. Because of this the application pool for the domain should be set to No Managed Code before installation.
To do that you will need to configure remote IIS access to your website and manage it trough that connection. For more details on how to configure that, please follow this TUTORIAL.
NOTE: If you are with a private server VPS/Cloud you can skip this part and proceed with opening your IIS service.
After you've made the preparations, please follow the steps below:
1. Connect to your website via the IIS Manager.
2. Click on Application Pools.
3. Right-click on the Application Pool your website is using and choose Basic Settings.
NOTE: One way to find out which application pool is being used is that it will have the number "1" under the Applications section.
4. In the new windows under .NET CLR version: you need to choose No Managed Code and click OK.
That's it, you can now proceed with your NopCommerce intallation.