Uncheck "Send the new user an email about their account." by default

uncheck_notify_register_on_new_user_form.php

add_action( 'user_new_form', 'fn_uncheck_notify_register_on_new_user_form' );
 
function fn_uncheck_notify_register_on_new_user_form() { 
    echo '<script>jQuery(document).ready(function($) { 
        $("#send_user_notification").removeAttr("checked"); 
    } ); </script>';
}