// src/Entity/User.php

namespace App\Entity;

use Doctrine\ORM\Mapping as ORM;

/**
 * @ORM\Entity
 */
class User
{
    // ...

    /**
     * @ORM\Column(type="boolean")
     */
    private $acceptTerms;

    // ...

    public function getAcceptTerms(): ?bool
    {
        return $this->acceptTerms;
    }

    public function setAcceptTerms(bool $acceptTerms): self
    {
        $this->acceptTerms = $acceptTerms;

        return $this;
    }

    // ...
}

// src/Form/UserType.php

namespace App\Form;

use App\Entity\User;
use Symfony\Component\Form\AbstractType;
use Symfony\Component\Form\FormBuilderInterface;
use Symfony\Component\OptionsResolver\OptionsResolver;
use Symfony\Component\Form\Extension\Core\Type\CheckboxType;

class UserType extends AbstractType
{
    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $builder
            // ...
            ->add('acceptTerms', CheckboxType::class, [
                'label' => '我接受服务条款',
                'required' => false,
            ])
            // ...
        ;
    }

    public function configureOptions(OptionsResolver $resolver)
    {
        $resolver->setDefaults([
            'data_class' => User::class,
        ]);
    }
}

{# templates/user/register.html.twig #}

<form action="{{ path('user_register') }}" method="POST">
    {{ form_widget(form.acceptTerms, {
        'attr': {
            'class': 'custom-checkbox',
        }
    }) }}
    <label for="{{ form.acceptTerms.vars.id }}">我接受服务条款</label>
    <button type="submit">注册</button>
</form>