Deprecated

D10 Upgrades from Drupal 9 can be tricky! There are usually unforeseen issues. Here are some commonly seen problems and solutions. 

The best place to find steps on how to upgrade: https://www.drupal.org/docs/upgrading-drupal/upgrading-from-drupal-8-or-later/upgrading-a-composer-based-site

replace

:$filesaved = file_save_data($file, $destination, FileSystemInterface::EXISTS_REPLACE);

With:

$fileRepository = \Drupal::service('file.repository');
$filesaved = $fileRepository->writeData($file, $destination, FileSystemInterface::EXISTS_REPLACE);