Answered Placeholder as link doesn't work

$newsite = "24";
$modx->setPlaceholder('mysite', $newsite);

$mychunk = $modx->getChunk('site-tpl');
 
$res = $modx->getObject('modResource',$id);
$res->set('content',$mychunk);
$res->save();

Here is my new site: <a href="[[~[[+mysite]]]]">My new Site</a><br>
TestID: [[+mysite]]

Here is my new site: <a href="">My new Site</a><br>
TestID: 24

<a href="index.php?id=[[+mysite]]">My New Site</a>

<a href="index.php?id=24">My New Site</a>

$newsite = "24";

$doc = $modx->newObject('modDocument');
$doc->set('parent', $id2);
$doc->set('pagetitle',$pagetitle7);

$doc->save();
$newsite = $doc->get('id');

/*--------- Work vom Formular abrufen ---------*/
$work = $_POST["work"]; 

if (isset($work)) {

// Erstellt die Überseite
      
    $pagetitle = $work;
    $parent = "0";
    $alias = "my-". $work;
    $template = 3;
    $richtext = 0;
    $published = true;

$doc = $modx->newObject('modDocument');
    $doc->set('parent',$parent);
    $doc->set('pagetitle',$pagetitle);
    $doc->set('alias',$alias);
    $doc->set('template',$template);
    $doc->set('published',$published);
    $doc->set('richtext',$richtext);    
    $doc->save();
    $id = $doc->get('id');


// Erstellt die Unterseite

    $pagetitle3 = "Arbeit 1";
    $template3 = "3";
    $alias3 = "meine-arbeiten";
    $published3 = true;
    $hidemenu3 = true;

    $doc = $modx->newObject('modDocument');
    $doc->set('parent', $id);
    $doc->set('pagetitle',$pagetitle3);
    $doc->set('alias',$alias3);
    $doc->set('template',$template3);
    $doc->set('published',$published3);
    $doc->set('hidemenu',$hidemenu3);
    $doc->save(); 
    $unterseiteid = $doc->get('id');


//  Bearbeitet den Content der Startseite und fügt Verlinkungen zu den Unterseiten ein
 
    $properties = array();
    $properties['unterseiteid'] = $unterseiteid;
    
    $mychunk = $modx->getChunk('kat-templates',$properties);
    echo $mychunk;

    $res = $modx->getObject('modResource',$id);
    $res->set('content',$mychunk);
    $res->save();

}

<h1>Überseite von Work</h1>
<a href="[[~[[+unterseiteid]]]]">Hier geht es direkt zu den einzelnen Arbeitsbereichen</a>

[[++site_url]][[!myFF? &tv=`uri` &id=`[[+unterseiteid]]`]]

$resourceId = 23; //$modx->resource->get('id') ??
$tvId = 12;
 
$query = $modx->newQuery('modTemplateVarResource', array(
    'contentid' => $resourceId,
    'tmplvarid' => $tvId,
));
$query->select('value');
$return $modx->getOption('site_url') . $modx->getValue($query->prepare());