.NET Core console application, how to configure appSettings per environment?

This is how we do it in our .netcore console app. The key here is to include the right dependencies on your project namely (may be not all, check based on your needs) and copy to output the appSetting.json as part of your buildoptions

  {
    "buildOptions": {
    "emitEntryPoint": true,
    "copyToOutput": {
       "include": [
       "appsettings*.json",
       "App*.config"
                 ]
          }
},

using Microsoft.Extensions.Configuration;
namespace MyApp
{
    public static void Main(string[] args)
    {
        var environmentName = Environment.GetEnvironmentVariable("ASPNETCORE_ENVIRONMENT");
       

        var builder = new ConfigurationBuilder()
            .AddJsonFile($"appsettings.json", true, true)
            .AddJsonFile($"appsettings.{environmentName}.json", true, true)
            .AddEnvironmentVariables();
        var configuration = builder.Build();
        var myConnString= configuration.GetConnectionString("SQLConn");
    }
}