如何发送主题有特殊字符的电子邮件？

when I send the email, if the subject says "Ç", it shows "?".

already tried to implement:

-charset="ascii";

-charset=UTF-8;

-$mail->$subject = "=?ISO-8859-1?Q?".imap_8bit("äöüßÄÖÜ sollte hier gehen")."?=";

-$mail->$subject = '=?UTF-8?B?'.base64_encode(utf8_encode("çççç")).'?=';

So far I can not solve this, what else can I do? I already searched in the forum has a lot of post to talk about it but none solved my problem.

My exemple code is :

$mail = new PHPMailer();
    $mail->charset="UTF-8";
    $mail->IsSMTP();
    $mail->Host = "*.*.*.*:*";
    $mail->SMTPAuth = false;
    $mail->From = "*@*.*";
    $mail->FromName = "newjob";  
    $mail->addAddress($add1, $addnome1);
    if($add2!=""){ $mail->addAddress($add2, $addnome2);};  
    if($add3!=""){ $mail->addAddress($add3, $addnome3);};  
    $mail->ContentType = 'text/calendar; charset=utf-8';
    $mail->$subject = "=?ISO-8859-1?Q?".imap_8bit("äöüßÄÖÜ")."?=";
    // $mail->$subject = '=?UTF-8?B?'.base64_encode(utf8_encode("çççç")).'?=';
    
    $ical = "BEGIN:VCALENDAR
";
    $ical .= "VERSION:2.0
";
    $ical .= "PRODID:-sigma.eda.pt
";
    $ical .= "METHOD:PUBLISH
";
    $ical .= "BEGIN:VEVENT
";
    $ical .= "ORGANIZER;SENT-BY=\"MAILTO:$add1
";
    $ical .= "ATTENDEE;CN=$add1;ROLE=REQ-PARTICIPANT;PARTSTAT=ACCEPTED;RSVP=false:mailto:$add1
";
    $ical .= "UID:".strtoupper(md5($event_id))."-sigma.eda.pt
";
    $ical .= "SEQUENCE:".$sequence."
";
    $ical .= "STATUS:".$status."
";
    $ical .= "DTSTAMPTZID=Europe/azores:".date('Ymd').'T'.date('His')."
";
    $ical .= "DTSTART:".$start."T".$start_time."
";
    $ical .= "DTEND:".$end."T".$end_time."
";
    $ical .= "LOCATION:".$venue."
";
    $ical .= "SUMMARY:".$summary."
";
    $ical .= "DESCRIPTION:".$descr."
";
    $ical .= "RRULE:FREQ=MONTHLY;INTERVAL=".$rotina.";COUNT=".$repete.";
";
    $ical .= "BEGIN:VALARM
";
    $ical .= "TRIGGER:-PT15M
";
    $ical .= "ACTION:DISPLAY
";
    $ical .= "DESCRIPTION:Reminder
";
    $ical .= "END:VALARM
";
    $ical .= "END:VEVENT
";
    $ical .= "END:VCALENDAR
";
    $mail->Body = $ical;
      try {
       if ( !$mail->Send() ) {
        //  $error = "Unable to send the email <br />";
        //  throw new phpmailerAppException($error);
       } else {
        //  echo 'Message has been sent<br /><br />';
       }
     } catch (phpmailerAppException $e) {
      //  $errorMsg[] = $e->errorMessage();
     }

EDIT image error from test:

here

</div>

PHP has case sensitive class properties, which means that when a property has a name CharSet, it has to be defined like this and not in lowercase $mail->charset. This also aplies to $mail->$subject and $mail->addAddress, addAddress case is like this. Here is an example with greek text that's working without any text conversion:

EDIT

I've tested this code above and it's working:

$email = 'some@email.com';
$message =  'Όνομα: <br/>'.
    'eMail: <br/>'.
    'Τηλέφωνο: <br/>'.
    '(Ç, ç, äöüßÄÖÜ sollte hier gehen, açores)';

use PHPMailer\PHPMailer\PHPMailer;
use PHPMailer\PHPMailer\Exception;

$mail = new PHPMailer(true);

try {
    $mail->isMail();
    $mail->addAddress($email);
    $mail->setFrom('test@email.com', 'Mailer');
    $mail->CharSet = PHPMailer::CHARSET_UTF8;
    $mail->Subject = "[ΣΥΜΜΕΤΟΧΗ] Νέα φόρμα δήλωσης συμμετοχής (Ç, ç, äöüßÄÖÜ sollte hier gehen, açores)";

    $mail->msgHTML($message);
    $mail->send();
    echo 'Message has been sent';
} catch(Exception $e) {
    echo "Message could not be sent. Mailer Error: {$mail->ErrorInfo}";
}

And here is the screenshot of the received email:

Result email screenshot