Thank so much for your response Joy. The wp-blog-header file is in the filemanager ftp. But in the plugin “code snippets” I have the option to just run the tag in the frontend.
I have tried it now with the 2 following codes. But still lighthouse and search console tell me the error concerning the missing viewport…
{
?>
<meta name="viewport" content="width=device-width, initial-scale=1">
<?php
};
<?php } );
add_action( 'wp_head', function () { ?>
<!meta name="viewport" content="width=device-width, initial-scale=1">
<?php } );
