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-includes/rest-api/class-wp-rest-server.php</b> on line <b>1831</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/rest-api/class-wp-rest-server.php</b> on line <b>1831</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/rest-api/class-wp-rest-server.php</b> on line <b>1831</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/rest-api/class-wp-rest-server.php</b> on line <b>1831</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/rest-api/class-wp-rest-server.php</b> on line <b>1831</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/rest-api/class-wp-rest-server.php</b> on line <b>1831</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/rest-api/class-wp-rest-server.php</b> on line <b>1831</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/rest-api/class-wp-rest-server.php</b> on line <b>1831</b><br />
{"id":71,"date":"2020-10-18T14:48:44","date_gmt":"2020-10-18T14:48:44","guid":{"rendered":"http:\/\/ibomberdefense.standardof.net\/wp-content\/uploads\/sites\/5\/2020\/10\/iBomber-Defense-Level-14-Germany-The-Final-Fight-1.jpg"},"modified":"2020-10-19T05:45:37","modified_gmt":"2020-10-19T05:45:37","slug":"ibomber-defense-level-14-germany-the-final-fight-1","status":"inherit","type":"attachment","link":"https:\/\/ibomberdefense.standardof.net\/th\/guide\/allied-campaign\/14-germany-the-final-fight\/ibomber-defense-level-14-germany-the-final-fight-1\/","title":{"rendered":"&#8220;iBomber Defense&#8221; &#8211; Level 14 &#8211; Germany: The Final Fight (1)"},"author":1,"featured_media":0,"comment_status":"open","ping_status":"closed","template":"","meta":{"_uag_custom_page_level_css":"","site-sidebar-layout":"default","site-content-layout":"","ast-site-content-layout":"default","site-content-style":"default","site-sidebar-style":"default","ast-global-header-display":"","ast-banner-title-visibility":"","ast-main-header-display":"","ast-hfb-above-header-display":"","ast-hfb-below-header-display":"","ast-hfb-mobile-header-display":"","site-post-title":"","ast-breadcrumbs-content":"","ast-featured-img":"","footer-sml-layout":"","ast-disable-related-posts":"","theme-transparent-header-meta":"","adv-header-id-meta":"","stick-header-meta":"","header-above-stick-meta":"","header-main-stick-meta":"","header-below-stick-meta":"","astra-migrate-meta-layouts":"default","ast-page-background-enabled":"default","ast-page-background-meta":{"desktop":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"tablet":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"mobile":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""}},"ast-content-background-meta":{"desktop":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"tablet":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"mobile":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""}}},"happyfiles_category":[22],"description":{"rendered":"<p class=\"attachment\"><a href='https:\/\/ibomberdefense.standardof.net\/wp-content\/uploads\/sites\/5\/2020\/10\/iBomber-Defense-Level-14-Germany-The-Final-Fight-1.jpg'><img decoding=\"async\" width=\"512\" height=\"288\" src=\"https:\/\/ibomberdefense.standardof.net\/wp-content\/uploads\/sites\/5\/2020\/10\/iBomber-Defense-Level-14-Germany-The-Final-Fight-1-512x288.jpg\" class=\"attachment-medium size-medium\" alt=\"&quot;iBomber Defense&quot; - Level 14 - Germany: The Final Fight (1)\" srcset=\"https:\/\/ibomberdefense.standardof.net\/wp-content\/uploads\/sites\/5\/2020\/10\/iBomber-Defense-Level-14-Germany-The-Final-Fight-1-512x288.jpg 512w, https:\/\/ibomberdefense.standardof.net\/wp-content\/uploads\/sites\/5\/2020\/10\/iBomber-Defense-Level-14-Germany-The-Final-Fight-1-800x450.jpg 800w, https:\/\/ibomberdefense.standardof.net\/wp-content\/uploads\/sites\/5\/2020\/10\/iBomber-Defense-Level-14-Germany-The-Final-Fight-1-200x113.jpg 200w, https:\/\/ibomberdefense.standardof.net\/wp-content\/uploads\/sites\/5\/2020\/10\/iBomber-Defense-Level-14-Germany-The-Final-Fight-1-768x432.jpg 768w, https:\/\/ibomberdefense.standardof.net\/wp-content\/uploads\/sites\/5\/2020\/10\/iBomber-Defense-Level-14-Germany-The-Final-Fight-1-16x9.jpg 16w, https:\/\/ibomberdefense.standardof.net\/wp-content\/uploads\/sites\/5\/2020\/10\/iBomber-Defense-Level-14-Germany-The-Final-Fight-1.jpg 1280w\" sizes=\"(max-width: 512px) 100vw, 512px\" \/><\/a><\/p>\n<p>Paths taken by the enemy units in the Germany level of &#8220;iBomber Defense.&#8221; Black line is for naval units and purple is for aircraft (arrows) the rest are ground (lines only).<\/p>\n"},"caption":{"rendered":"<p>Paths taken by the enemy units in the Germany level of &#8220;iBomber Defense.&#8221; Black line is for naval units and purple is for aircraft (arrows) the rest are ground (lines only).<\/p>\n"},"alt_text":"\"iBomber Defense\" - Level 14 - Germany: The Final Fight (1)","media_type":"image","mime_type":"image\/jpeg","media_details":{"width":1280,"height":720,"file":"2020\/10\/iBomber-Defense-Level-14-Germany-The-Final-Fight-1.jpg","sizes":{"medium":{"file":"iBomber-Defense-Level-14-Germany-The-Final-Fight-1-512x288.jpg","width":512,"height":288,"mime_type":"image\/jpeg","source_url":"https:\/\/ibomberdefense.standardof.net\/wp-content\/uploads\/sites\/5\/2020\/10\/iBomber-Defense-Level-14-Germany-The-Final-Fight-1-512x288.jpg"},"large":{"file":"iBomber-Defense-Level-14-Germany-The-Final-Fight-1-800x450.jpg","width":800,"height":450,"mime_type":"image\/jpeg","source_url":"https:\/\/ibomberdefense.standardof.net\/wp-content\/uploads\/sites\/5\/2020\/10\/iBomber-Defense-Level-14-Germany-The-Final-Fight-1-800x450.jpg"},"thumbnail":{"file":"iBomber-Defense-Level-14-Germany-The-Final-Fight-1-200x113.jpg","width":200,"height":113,"mime_type":"image\/jpeg","source_url":"https:\/\/ibomberdefense.standardof.net\/wp-content\/uploads\/sites\/5\/2020\/10\/iBomber-Defense-Level-14-Germany-The-Final-Fight-1-200x113.jpg"},"medium_large":{"file":"iBomber-Defense-Level-14-Germany-The-Final-Fight-1-768x432.jpg","width":768,"height":432,"mime_type":"image\/jpeg","source_url":"https:\/\/ibomberdefense.standardof.net\/wp-content\/uploads\/sites\/5\/2020\/10\/iBomber-Defense-Level-14-Germany-The-Final-Fight-1-768x432.jpg"},"trp-custom-language-flag":{"file":"iBomber-Defense-Level-14-Germany-The-Final-Fight-1-16x9.jpg","width":16,"height":9,"mime_type":"image\/jpeg","source_url":"https:\/\/ibomberdefense.standardof.net\/wp-content\/uploads\/sites\/5\/2020\/10\/iBomber-Defense-Level-14-Germany-The-Final-Fight-1-16x9.jpg"},"full":{"file":"iBomber-Defense-Level-14-Germany-The-Final-Fight-1.jpg","width":1280,"height":720,"mime_type":"image\/jpeg","source_url":"https:\/\/ibomberdefense.standardof.net\/wp-content\/uploads\/sites\/5\/2020\/10\/iBomber-Defense-Level-14-Germany-The-Final-Fight-1.jpg"}},"image_meta":{"aperture":"0","credit":"","camera":"","caption":"","created_timestamp":"0","copyright":"","focal_length":"0","iso":"0","shutter_speed":"0","title":"","orientation":"0","keywords":[]}},"post":304,"source_url":"https:\/\/ibomberdefense.standardof.net\/wp-content\/uploads\/sites\/5\/2020\/10\/iBomber-Defense-Level-14-Germany-The-Final-Fight-1.jpg","_links":{"self":[{"href":"https:\/\/ibomberdefense.standardof.net\/th\/wp-json\/wp\/v2\/media\/71"}],"collection":[{"href":"https:\/\/ibomberdefense.standardof.net\/th\/wp-json\/wp\/v2\/media"}],"about":[{"href":"https:\/\/ibomberdefense.standardof.net\/th\/wp-json\/wp\/v2\/types\/attachment"}],"author":[{"embeddable":true,"href":"https:\/\/ibomberdefense.standardof.net\/th\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/ibomberdefense.standardof.net\/th\/wp-json\/wp\/v2\/comments?post=71"}],"wp:term":[{"taxonomy":"happyfiles_category","embeddable":true,"href":"https:\/\/ibomberdefense.standardof.net\/th\/wp-json\/wp\/v2\/happyfiles_category?post=71"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}