Change the next and previous post links sort order for single espresso_events post types. Requires EE4 + a theme that uses the native next_post_link() and previous_post_link() functions.

adjacent_posts.php

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

function ee_custom_adjacent_post() {
    add_filter( 'get_next_post_join', 'ee_custom_adjacent_post_join' );
    add_filter( 'get_previous_post_join', 'ee_custom_adjacent_post_join' );
    add_filter( 'get_next_post_where', 'ee_custom_adjacent_post_where' );
    add_filter( 'get_previous_post_where', 'ee_custom_adjacent_post_where' );
    add_filter( 'get_next_post_sort', 'ee_custom_adjacent_post_sort' );
    add_filter( 'get_previous_post_sort', 'ee_custom_adjacent_post_sort' );
}
add_action( 'template_redirect', 'ee_custom_adjacent_post' );

function ee_custom_adjacent_post_join($sql) {
    global $wpdb;
    if ( !is_main_query() || !is_singular( 'espresso_events' ) ) {
        return $sql;
    }
    $sql .= ' INNER JOIN ' . EEM_Datetime::instance()->table() . ' ON ( p.ID = ' . EEM_Datetime::instance()->table() . '.' . EEM_Event::instance()->primary_key_name() . ' ) ';
    return $sql;
}
function ee_custom_adjacent_post_where($sql) {
    global $wpdb, $post;
    if ( !is_main_query() || !is_singular( 'espresso_events' ) ) {
        return $sql;
    }
    // Pull the datetimes for this event order by start_date/time
    $datetimes = EEM_Datetime::instance()->get_datetimes_for_event_ordered_by_start_time( $post->ID, true, false );
    // Get the last datetime and use that one.
    $datetime = end( $datetimes );
        if ( $datetime instanceof EE_Datetime ) {   
            $current_event_start_date = $datetime->get_raw('DTT_EVT_start');
            $current_event_start_date = date( 'Y-m-d H:i:s', $current_event_start_date );
            if ( current_filter() == 'get_next_post_where' ) { 
                $compare = '>';
            } else {
                $compare = '<';
            }
            $sql =  " WHERE {$wpdb->prefix}esp_datetime.DTT_EVT_start {$compare} '" . $current_event_start_date . "' AND p.post_type = 'espresso_events' AND ( p.post_status = 'publish' ) ";
        }    
    return $sql;
}
function ee_custom_adjacent_post_sort($sql) {
    global $wpdb;
    if ( !is_main_query() || !is_singular( 'espresso_events' ) ) {
        return $sql;
    }
    if ( current_filter() == 'get_next_post_sort' ) { 
        $sort = 'ASC';
    } else {
        $sort = 'DESC';
    }
    $sql = " ORDER BY {$wpdb->prefix}esp_datetime.DTT_EVT_start {$sort} LIMIT 1";
    return $sql;
}