if ( ! function_exists( 'wpcodebook_add_user_id_column' ) ) {
    /**
     * Adds "ID" column to the "Users" page.
     */
    function wpcodebook_add_user_id_column( $columns ) {
        $columns['user_id'] = __( 'ID', 'text-domain' );
        return $columns;
    }
    add_filter( 'manage_users_columns', 'wpcodebook_add_user_id_column' );
}

if ( ! function_exists( 'wpcodebook_render_user_id_column' ) ) {
    /**
     * Renders "ID" column.
     */
    function wpcodebook_render_user_id_column( $output, $column_name, $user_id ) {
        return ( 'user_id' === $column_name ? $user_id : $output );
    }
    add_filter( 'manage_users_custom_column', 'wpcodebook_render_user_id_column', 10, 3 );
}