Do you have default values set for completed_at and updated_at?
In your migration, both of these fields are marked as nullable, so you should make them nullable in your Data class as well, like this:

public function __construct(
    public User $creator,
    public TaskCategory $taskCategory,
    public TaskPriorityEnum $priority,
    public string $title,
    public string $slug,
    public string $content,
    public bool $completed,
    public ?\DateTime $completed_at,
    public ?\Date $deadline_at,
    public \DateTime $created_at,
    public ?\DateTime $updated_at,
)

also u can try ?\Carbon\Carbon