Use DebugBar (v2020)

Hi all,
for debugging I use already kind via composer which works like a charm.Also I’d like to use DebugBar => http://phpdebugbar.com/

I add the composer package via menue/ tools => composer packages and generade all new.Integration Header => <?php echo $debugbarRenderer->renderHead() (deploy js scripts and css)start new objekt in global code:
$debugbar = new StandardDebugBar();
$debugbarRenderer = $debugbar->getJavascriptRenderer();and try to call the objekt in Page_Rendering() Event.but no success:
Notice: Undefined variable: debugbarRenderer in /var/www/imostar/userfn.php on line 139 (whis is the line from Page_Rendering() Event)any idea?

You may read Using namespaces: Basics.