Completely disables comments on a Wordpress site.

wp_disable_comments.php

<?php

if (!class_exists(WP_Disable_Comments)) {
    class WP_Disable_Comments
    {

        private static $instance = null;

        public static function get_instance()
        {
            if (self::$instance === null) {
                self::$instance = new self();
            }
            return self::$instance;
        }

        private function __construct()
        {
            $this->init_hooks();
        }

        private function init_hooks()
        {
            add_action('admin_init', [$this, 'disable_admin_comments']);
            add_filter('comments_open', '__return_false', 20, 2);
            add_filter('pings_open', '__return_false', 20, 2);
            add_filter('comments_array', '__return_empty_array', 10, 2);
            add_action('admin_menu', [$this, 'remove_comments_admin_menu']);
            add_action('init', [$this, 'remove_admin_bar_comments']);
            add_filter('rest_endpoints', [$this, 'disable_rest_api_comments']);
        }

        public function disable_admin_comments()
        {
            global $pagenow;

            if ($pagenow === 'edit-comments.php') {
                wp_safe_redirect(admin_url());
                exit;
            }

            remove_meta_box('dashboard_recent_comments', 'dashboard', 'normal');

            foreach (get_post_types() as $post_type) {
                if (post_type_supports($post_type, 'comments')) {
                    remove_post_type_support($post_type, 'comments');
                    remove_post_type_support($post_type, 'trackbacks');
                }
            }
        }

        public function remove_comments_admin_menu()
        {
            remove_menu_page('edit-comments.php');
        }

        public function remove_admin_bar_comments()
        {
            if (is_admin_bar_showing()) {
                remove_action('admin_bar_menu', 'wp_admin_bar_comments_menu', 60);
            }
        }

        public function disable_rest_api_comments($endpoints)
        {
            if (isset($endpoints['/wp/v2/comments'])) {
                unset($endpoints['/wp/v2/comments']);
            }

            if (isset($endpoints['/wp/v2/comments/(?P<id>[\d]+)'])) {
                unset($endpoints['/wp/v2/comments/(?P<id>[\d]+)']);
            }

            return $endpoints;
        }
    }

    WP_Disable_Comments::get_instance();
}