The framework 'Microsoft.AspNetCore.App', version '3.1.3' was not found
I have posted same question on github dotnet issues page, the user vitek karas provided me the lead that x64 runtime
C:\ProgramFiles\dotnet\shared\Microsoft.AspNetCore.App\3.1.3 folder was missing.
Then I tried reinstalling SDK 3.1.201 still folder was missing.
I also tried install aspnetcore-runtime-3.1.3 X64 still folder was missing.
finally I have downloaded dotnet-sdk-3.1.201-win-x64.zip and copied
Microsoft.AspNetCore.App\3.1.3 folder manually from the zip file to
C:\ProgramFiles\dotnet\shared\Microsoft.AspNetCore.App\3.1.3 then my asp.net core application started working .
I solved the problem by installing the Hosting bundle from here.