Ticket #46338: chat-post-type.php

<?php
/*
 * Plugin Name: Chat Custom Post Type
 */

class Chat_Post_Type {

        public static $post_type = 'tg_chat';

        const AD_GROUPS_TAXONOMY_SLUG = 'groups';

        public static function init() {
                add_action( 'init', [ __CLASS__, 'action_register_taxonomy' ] );
                add_action( 'init', [ __CLASS__, 'action_register_post_type' ] );
        }

        public static function action_register_taxonomy() {
                register_taxonomy(
                        self::AD_GROUPS_TAXONOMY_SLUG,
                        self::$post_type,
                        [
                                'label'              => 'AD Groups',
                                'public'             => true,
                                'show_in_rest'       => false,
                                'publicly_queryable' => false,
                                // This line causes a fatal error when saving Quick Edit:
                                'meta_box_cb'        => 'post_categories_meta_box'
                        ]
                );
        }

        public static function action_register_post_type() {
                $args = [
                        'label'               => 'Chat',
                        'supports'            => [ 'title', 'custom-fields' ],
                        'taxonomies'          => [ self::AD_GROUPS_TAXONOMY_SLUG ],
                        'hierarchical'        => false,
                        'public'              => false,
                        'show_ui'             => true,
                        'show_in_menu'        => true,
                        'show_admin_column'   => true,
                        'menu_position'       => 24,
                        'menu_icon'           => 'dashicons-groups',
                        'show_in_admin_bar'   => false,
                        'show_in_nav_menus'   => false,
                        'can_export'          => true,
                        'has_archive'         => false,
                        'exclude_from_search' => true,
                        'publicly_queryable'  => true,
                        'capability_type'     => 'page',
                ];

                register_post_type( self::$post_type, $args );
        }
}

Chat_Post_Type::init();