The "file_validate_extensions" plugin has been deprecated in 10.2.x

Here's a similar situation and fix: 🐛 The "file_validate_extensions" Plugin Has Been Deprecated in 10.2.x Active

Definitly!

No, this was correctly adjusted for the D11 release:

    if (version_compare(\Drupal::VERSION, '11', '>=')) {
      $uploadValidators['FileExtension']['extensions'] = $originalExtension;
    }
    // @todo Remove this, once we drop the Drupal 10 support:
    else {
      $uploadValidators['file_validate_extensions'] = [$originalExtension];
    }
  }

Closing this.

Perfect, thanks for the check @grevil!