Change the Events RSS feed pubDate for each event item. Event Espresso 4.

events_rss.php

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

function change_post_time_to_event_start($time, $d, $gmt) {
    global $post;
    $event = EEH_Event_View::get_event($post->ID);
    if($event instanceof EE_Event) {
        $primary_datetime = clone $event->primary_datetime();
        $time = $primary_datetime->start_date_and_time('Y-m-d', 'H:i:s'); 
    }
    return $time;       
}

add_action('rss2_ns','extra_feed_type_event');
function extra_feed_type_event(){
    if (EE_Registry::instance()->REQ->is_set('post_type')) {
        if(EE_Registry::instance()->REQ->get('post_type') == 'espresso_events') {
            echo 'xmlns:ev="http://purl.org/rss/1.0/modules/event/"';
            add_filter('get_post_time', 'change_post_time_to_event_start', 10, 3);
        }
    }
}