Unable to create an object of type 'MyContext'. For the different patterns supported at design time

I Resolved this by just adding a plain constructor to my Context

public class DataContext : DbContext
{
    public DataContext()
    {
    }

    public DataContext(DbContextOptions options) : base(options)
    {
    }

    protected override void OnConfiguring(DbContextOptionsBuilder options)
    {
        if (!options.IsConfigured)
        {
            options.UseSqlServer("A FALLBACK CONNECTION STRING");
        }
    }
    
    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        base.OnModelCreating(modelBuilder);            
    }
}

I came across this problem today. In my case, the SqlDbContext was in a separate ASP.Net Core 3.1 class library project, and I was trying to setup migrations using the dotnet CLI from that project's root folder. The main web application, which is the default project, contains the connection string configuration inside the appsettings.json and the startup configurations therefore I had to specify the startup project path using the -s switch as follows.

>dotnet ef migrations add initialcreation -s ..\MyWebApp\MyWebApp.csproj

-s, short for startup project, is a quick alternative to implementing IDesignTimeDbContextFactory when the DbContext is in a different project than the web application project.

I've had same problem as You. Maybe it was not for a Console Application but error was the same. So i thought that it is worth to share with my answer. I was using NET Core 3.0 and to fix the problem I have to change the IHostBuilder into IWebHost and then everything was fine. The problem was in class Program.

public static void Main(string[] args)
    {
        CreateHostBuilder(args).Build().Run();
    }

    public static IHostBuilder CreateHostBuilder(string[] args) =>
        Host.CreateDefaultBuilder(args)
            .ConfigureWebHostDefaults(webBuilder =>
            {
                webBuilder.UseStartup<Startup>();
            });

into

public static void Main(string[] args)
    {
        BuildWebHost(args).Run();
    }

    public static IWebHost BuildWebHost(string[] args) =>
    WebHost.CreateDefaultBuilder(args)
        .UseStartup<Startup>()
        .Build();