Error in app.config

i m facing below exception in console application

An unhandled exception of type 'System.IO.FileNotFoundException' occurred in mscorlib.dll

Additional information: Could not load file or assembly 'netstandard, Version=2.1.0.0, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51' or one of its dependencies. The system cannot find the file specified.

here is app.config

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  
  
  <configSections>
        <!-- For more information on Entity Framework configuration, visit http://go.microsoft.com/fwlink/?LinkID=237468 -->
        <section name="entityFramework"
          type="System.Data.Entity.Internal.ConfigFile.EntityFrameworkSection, EntityFramework, Version=6.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"
          requirePermission="false"/>
    </configSections>
  <connectionStrings>

    <add name="NinjaDatabase" connectionString="Data Source=.;Initial Catalog=NinjaDatabase;Integrated Security=true" providerName="System.Data.SqlClient"/>

    <!--<add name="DefaultConnection" connectionString="Data Source=(LocalDb)\MSSQLLocalDB;AttachDbFilename=|DataDirectory|\aspnet-ForEF-20200630045341.mdf;Initial Catalog=aspnet-ForEF-20200630045341;Integrated Security=True" providerName="System.Data.SqlClient" />-->
  </connectionStrings>
    <startup> 
        <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.5.1"/>
    </startup>
    <entityFramework>
        <providers>
            <provider invariantName="System.Data.SqlClient" type="System.Data.Entity.SqlServer.SqlProviderServices, EntityFramework.SqlServer"/>
        </providers>
    </entityFramework>
</configuration>

Thnaks