add_action('init', function() {
    if (!isset($_GET['delete_posts'])) return;

    global $wpdb;

    $batch = 5000;

    $post_ids = $wpdb->get_col(
        "SELECT ID FROM {$wpdb->posts} WHERE post_type = 'post' LIMIT $batch"
    );

    if (empty($post_ids)) {
        echo "Done.";
        exit;
    }

    $ids_str = implode(',', array_map('intval', $post_ids));

    $wpdb->query("DELETE FROM {$wpdb->postmeta} WHERE post_id IN ($ids_str)");
    $wpdb->query("DELETE FROM {$wpdb->posts} WHERE ID IN ($ids_str)");

    echo count($post_ids) . " posts deleted.";
    exit;
});
<br />
<b>Warning</b>:  Cannot modify header information - headers already sent by (output started at /home/standa9/public_html/wp-content/mu-plugins/index.php:1) in <b>/home/standa9/public_html/wp-content/plugins/wp-force-ssl/wp-force-ssl.php</b> on line <b>932</b><br />
<br />
<b>Warning</b>:  Cannot modify header information - headers already sent by (output started at /home/standa9/public_html/wp-content/mu-plugins/index.php:1) in <b>/home/standa9/public_html/wp-includes/feed-rss2.php</b> on line <b>8</b><br />
<?xml version="1.0" encoding="UTF-8"?><rss version="2.0"
	xmlns:content="http://purl.org/rss/1.0/modules/content/"
	xmlns:wfw="http://wellformedweb.org/CommentAPI/"
	xmlns:dc="http://purl.org/dc/elements/1.1/"
	xmlns:atom="http://www.w3.org/2005/Atom"
	xmlns:sy="http://purl.org/rss/1.0/modules/syndication/"
	xmlns:slash="http://purl.org/rss/1.0/modules/slash/"
	 xmlns:media="http://search.yahoo.com/mrss/" >

<channel>
	<title>Darwinia Strategy Guide</title>
	<atom:link href="https://darwinia.standardof.net/de/feed/" rel="self" type="application/rss+xml" />
	<link>https://darwinia.standardof.net/de/</link>
	<description></description>
	<lastBuildDate>Do, 12. November 2020 00:09:12 +0000</lastBuildDate>
	<language>de</language>
	<sy:updateperiod>
	stündlich	</sy:updateperiod>
	<sy:updatefrequency>
	1	</sy:updatefrequency>
	<generator>https://wordpress.org/?v=6.5.10</generator>

<image>
	<url>https://darwinia.standardof.net/wp-content/uploads/sites/7/2020/10/cropped-Darwinia-Icon-1-32x32.png</url>
	<title>Darwinia Strategy Guide</title>
	<link>https://darwinia.standardof.net/de/</link>
	<width>32</width>
	<height>32</height>
</image> 
</channel>
</rss>