How to hint to Doctrine / Unit of Work that we are working with existing data after serialization?

Question

Doctrine ORM

We have an entity, we get it from the database

public function find(string $id): ?DomainEntity {
        /** @var DoctrineEntity|null $entity */
        $entity = $this->findOneBy(['id' => $id]);
        if (true === $entity instanceof DoctrineEntity) {
            $entity = $this->coverter->covertDoctrineToDomainEntity($entity);
        }
        return $entity;
    }

The service that uses DomainEntity converts it back to

$entity = $this->coverter->covertDomainEntityToDoctrine($domainEntity);

And this is where the problems begin, because after the first conversion covertDoctrineToDomainEntity

$entityManger->persist(this->coverter->covertDomainEntityToDoctrine($domainEntity);

unit of work loses connection. Converting a doctrine entity to any other object, serializing it, and other similar actions are tantamount to deleting it from the cache, UoW memory

$entityManger->clear(DoctrineEntity::class);
        $entityManger->detach($doctrineEntity);
        $entityManger->remove($doctrineEntity);

under the hood
$this->unitOfWork->remove($entity);

This causes Doctrine 2 to treat the entity as a new entity and insert it as a new entity. Duplicate Entry Exception

So, how to hint to the doctrine, unit of work, that we are dealing with an already existing object?