If you face “Argument 1 passed to App\Service\FileUploader::upload() must be an instance of Symfony\Component\HttpFoundation\File\UploadedFile, string given, ” this error while playing with files in Symfony 4. Then you need to change your file field in controller as. Change your code from
$file = $task->getTaskLogo();to
$file = $form['task_logo']->getData();. Where task_logo is the name of the file field of your form.