It still means nothing. How can I help you, if I don't know what have you done? There could be a million reasons - for example missing permissions, error in configuration, a typo in any file of the solution, missing files in the solution, and so on. Please give us an error log from the stdout folder. Without it, we are not able to track the issue, we are not clairvoyants.

Enable the stdout logs in web.config file, 7th line - and change the stdoutLogEnabled="false" to stdoutLogEnabled="true" and run the application again.

Hi,
Please install Hosting Bundle for .Net Core 3.1 :
https://dotnet.microsoft.com/download/dotnet-core/3.1

Regards
Krzysztof