To create a custom Symfony validator, follow these steps:
Create a new class that extends Symfony\Component\Validator\Constraint or Symfony\Component\Validator\ConstraintValidator.
Implement the methods required by the base class. For a custom constraint class, you need to implement the public property $message and the public property $payload at least. For a custom validator class, you need to implement the validate() method.
In the custom constraint class, you can define any additional properties and methods that are required for your validation logic. You can also define the needed constraints by implementing the Symfony\Component\Validator\ConstraintValidatorInterface interface.
Register your custom validator as a service in your Symfony application (either in services.yaml or in a custom service configuration file).
Use your custom validator in your Symfony application by annotating your entity or form field with the custom constraint you created.
For more detailed information and examples, you can refer to the Symfony documentation on custom validators: https://symfony.com/doc/current/validation/custom_constraint.html