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;
});
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<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/rest-api/class-wp-rest-server.php</b> on line <b>1831</b><br />
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<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/rest-api/class-wp-rest-server.php</b> on line <b>1831</b><br />
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<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/rest-api/class-wp-rest-server.php</b> on line <b>1831</b><br />
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<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/rest-api/class-wp-rest-server.php</b> on line <b>1831</b><br />
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<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/rest-api/class-wp-rest-server.php</b> on line <b>1831</b><br />
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<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/rest-api/class-wp-rest-server.php</b> on line <b>1831</b><br />
{"id":60,"count":2,"description":"","link":"https:\/\/solar2.standardof.net\/tl\/category\/giveaway\/","name":"Pagbibigay","slug":"pamigay","taxonomy":"category","parent":0,"meta":[],"_links":{"self":[{"href":"https:\/\/solar2.standardof.net\/tl\/wp-json\/wp\/v2\/categories\/60"}],"collection":[{"href":"https:\/\/solar2.standardof.net\/tl\/wp-json\/wp\/v2\/categories"}],"about":[{"href":"https:\/\/solar2.standardof.net\/tl\/wp-json\/wp\/v2\/taxonomies\/category"}],"wp:post_type":[{"href":"https:\/\/solar2.standardof.net\/tl\/wp-json\/wp\/v2\/posts?categories=60"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}