$_POST values are available but cannot be accessed

I try to submit a form via AJAX and then work with the values. Here is the markup of the form:

<form id="formDeb" action="controller/processDeb.php" method="POST" enctype="multipart/form-data">
    <div class="row">
        <div class="col-md-6">
            <div class="form-group">
                <label for="formGroupName">Angezeigter Name in Cydia/Sileo</label>
                <input type="text" class="form-control" id="formGroupName" name="formGroupName"
                       placeholder="Vorname Nachname oder K&uuml;rzel">
            </div>
        </div>
        <div class="col-md-6">
            <div class="form-group">
                <label for="formGroupMail">Deine E-Mail Adresse</label>
                <input type="email" class="form-control" id="formGroupMail" name="formGroupMail"
                       placeholder="Deine E-Mail Adresse">
            </div>
        </div>
    <!-- and more fields --> 
</form>

I submit the form via Ajax:

var myFormData = new FormData(this);
var supportedDevices = getSelectedBoxes("devices");
var supportedVersions = getSelectedBoxes("iosversions");

myFormData.append("supportedDevices", supportedDevices);
myFormData.append("supportedVersions", supportedVersions);

$.ajax({
    type: method,
    url: targetUrl,
    data: myFormData,
    processData: false,
    async: true,
    beforeSend: function () {
       isSubmitting = true;

       $btnSubmit.attr('disabled', 'true');
       $btnImg.toggle();
       $btnLoader.toggle();
     }
})

in the processDeb.php File i have this code:

if ($_SERVER["REQUEST_METHOD"] == "POST") {
if (is_array($_POST)) {
    echo '<pre>' . var_export($_POST, true) . '</pre>';
    $name = $_POST['cName'] ?? '';
    $mail = $_POST['cMailAddress'] ?? '';
}

The values are should be set, but when I try to access $name or $mail the content is ''.

The output of the var_export is the following:

array ( '------WebKitFormBoundaryMBXZo8GpgumN5Etl Content-Disposition:_form-data;_name' => '"formGroupName"

fancy name ------WebKitFormBoundaryMBXZo8GpgumN5Etl Content-Disposition: form-data; name="formGroupMail"

[email protected]

So it should be possible to access the values using $_POST['formGroupName'] but it is not possible.

The enctype is set to multipart/form-data because there are also some upload fields for the user.