How to retrieve information from a file with an html form?

I have a problem with my form.

This is the situation:
I use the CraueFormFlowBundle bundle to create a step-by-step form (4 steps).

So, I use the create form of the bundle $form = $flow->createForm(); to create the form.

But when I set up the Symfony file uploader, I can't get the information from the file.

Does anyone have a solution or even a small lead?

My controller:

/**
  * @Route("/classified/new", name="classified_create")
  * @IsGranted("ROLE_USER")
  * @param Request $request
  * @param ObjectManager $manager
  * @param CreateVehicleFlow $createVehicleFlow
  * @param FileUploader $fileUploader
  * @return Response
 */
 public function create(Request $request, ObjectManager $manager, CreateVehicleFlow $createVehicleFlow, FileUploader $fileUploader)
 {
     $user = $this->getUser();
     $vehicle = new Vehicle();
     $vehicle->setCity($user->getCity());
     $vehicle->setAuthor($user);

     $flow = $createVehicleFlow;
     $flow->setGenericFormOptions([
         'action' => $this->generateUrl('classified_create')
     ]);
     $flow->bind($vehicle);
     $form = $flow->createForm();
     if ($flow->isValid($form)) {
         $flow->saveCurrentStepData($form);
         if ($flow->nextStep()) {
             $form = $flow->createForm();
         } else {
             foreach ($vehicle->getImages() as $image) {
                 $image->setVehicle($vehicle);
                    $manager->persist($image);
                 }
                 /** @var UploadedFile $imageCoverFile */
                 $imageCoverFile = $form['imageCover']->getData();

                 if ($imageCoverFile) {
                     $imageCoverFileName = $fileUploader->upload($imageCoverFile);
                     $vehicle->setImageCoverName($imageCoverFileName);
                 }

                 $manager->persist($vehicle);
                 $manager->flush();

                 $flow->reset();

                 $this->addFlash(
                     'success',
                     "Votre annonce <i>{$vehicle->getId()}</i> a bien été enregistrée"
                 );

                 return $this->redirect($this->generateUrl('account_index'));
             }
         }

         return $this->render('front/classified/new_vehicle.html.twig', [
             'form' => $form->createView(),
             'flow' => $flow,
             'vehicle' => $vehicle,
         ]);
     }

My form type:

->add(
    'imageCover',
    FileType::class, [
        'label' => 'Image de couverture',
        'mapped' => false,
        'required' => false,
        'constraints' => [
            new File([
                'maxSize' => '3M',
                'mimeTypes' => [
                    'application/jpeg',
                    'application/png',
                ],
                'mimeTypesMessage' => 'Vous devez télécharger un format valide'
            ])
        ]
    ]
);

My entity: I am only the name of the file that is in my entity and only the name of the file that is saved in the database.

/**
 * @ORM\Column(type="string", length=255)
*/
private $imageCoverName;

public function getImageCoverName(): ?string
{
   return $this->imageCoverName;
}

public function setImageCoverName(string $imageCoverName): self
{
   $this->imageCoverName = $imageCoverName;

   return $this;
}

I have tried this solution but nothing works.

$imageCoverFile = $form['createVehicle']['imageCover']->getData();