<?php
use PHPMailer\PHPMailer\PHPMailer;
use PHPMailer\PHPMailer\Exception;

//require
require'PHPMailer/src/Exception.php';
require'PHPMailer/src/PHPMailer.php';
require'PHPMailer/src/SMTP.php';


//Creation de l& variable mail objet phpmailer
function sendmail($sujet,$message,$expediteur){

$mail = new PHPMailer(true);

try {
//Server settings
$mail->SMTPDebug = SMTP::DEBUG_SERVER; //Enable verbose debug output
$mail->isSMTP(); //Send using SMTP
$mail->Host = 'smtp.orange.fr'; //Set the SMTP server to send through
$mail->SMTPAuth = true; //Enable SMTP authentication
$mail->Username = 'mon adresse mail'; //SMTP username
$mail->Password = 'mot de passe ; //SMTP password
$mail->SMTPSecure = PHPMailer::ENCRYPTION_SMTPS; //Enable implicit TLS encryption
//$mail->SMTPSecure = 'SSL';
// dans video c'est //$mail->SMTPSecure = 'ssl'; //Enable implicit TLS encryption
$mail->Port = 465;

Merci pour le tuto, je pense l'avoir suivi a la lettre,
[...]
La ligne 18 c'est :

    $mail->SMTPDebug = SMTP::DEBUG_SERVER;