Add a noindex meta tag to expired Event Espresso 4 events. Useful for SEO.

robots_expired.php

<?php
//* Please do NOT include the opening php tag, except of course if you're starting with a blank file

function ee_add_tagseo_meta() {
    if ('espresso_events' == get_post_type() && is_single() ){
        $id = get_the_id();
        $event = EEH_Event_View::get_event( $id );
        $status = $event instanceof EE_Event ? $event->get_active_status() : '';
        if ( $status == 'DTE' ) {
            echo '<meta name="robots" content="noindex">';
        }
    }
}
add_action( 'wp_head', 'ee_add_tagseo_meta', 9 );