Starting with Laravel 8, you no longer need to set the $model property on model factories when it may be guessed through Laravel conventions.

Before

class PostFactory extends Factory
{
    /**
     * The name of the factory's corresponding model.
     *
     * @var string
     */
    protected $model = \App\Models\Post::class;
 
    // ...
}

After

class PostFactory extends Factory
{
    // ...
}