How to load a file entity by uuid?

So I am trying to use the default image for users in a menu block if a custom one does not exist. And for it I am getting the image file uuid:

$default_image = $user->get('user_picture')->getSetting('default_image');

Then loading the file entity:

$file = Drupal::service('entity.repository')->loadEntityByUuid('file', $default_image['uuid']);

This is returning null. What am I doing wrong? And is there a better way to achieve this?

This might be what you need?

use Drupal\field\Entity\FieldConfig;
use Drupal\image\Entity\ImageStyle;

if (FieldConfig::loadByName('user', 'user', $imageFieldName)
  ->getSetting('default_image')['uuid']) {

  $imageStyle = ImageStyle::load('thumbnail');

  // Load the default image settings.
  $imageGetSettings = FieldConfig::loadByName('user', 'user', $imageFieldName)
    ->getSetting('default_image');

  // Get the default image URI from settings.
  $imageURI = Drupal::service('entity.repository')
    ->loadEntityByUuid('file', $imageGetSettings['uuid'])
    ->getFileUri();

  // Build image style path.
  $imageStyleURL = $imageStyle->buildUrl($imageURI);

  // Set $imageURL.
  $imageURL = file_url_transform_relative($imageStyleURL);
}