using (IServiceScope scope = host.Services.CreateScope())
{
    AppDbContext dbCtx = scope.ServiceProvider.GetRequiredService<AppDbContext>();
    dbCtx.Database.Migrate();
    if (!dbCtx.Products.Any())
    {
        dbCtx.Products.Add(
            new Product
            {
                Name = "the Name",
                Description = "the Description"
            });
        dbCtx.SaveChanges();
    }
}

modelBuilder.Entity<Product>().HasData(
    new Product
    {
        Id = 1,
        Name = "the Name",
        Description = "the Description"
    });