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' ) {
?>
<meta name="robots" content="noindex">
<?php
    }
  }
}
add_action( 'wp_head', 'ee_add_tagseo_meta', 9 );