if (strlen($file
 ->getFilename()) > 100) {
    $errors[] = t("The file's name exceeds the 100 characters limit.");
 }

use DrupalCoreFormFormStateInterface;
 function blank_moda_file_validate(DrupalfileFileInterface $file) {
   $errors = array();

if ($file
 ->getMimeType()) !== jpg, gif) {
   $errors[] = t("The file is not a jpg or gif.");
}