TEC > Next and previous links on the single event page point to the next event in the event's category

functions.php

<?php
/**
 * Next and previous links on the single event page point to the next event in the event's category.
 * If an event has no categories, it will show the next event, regardless of any categories.
 * If an event has multiple categories, it will show the next event which has any of the categories.
 *   After that, it will show events having categories of this event.
 *
 * Usage: Add the snippet with Code Snippets or to your functions.php file.
 *
 * @author: Andras Guseo
 *
 * Plugins required: The Events Calendar
 *
 * @since May 12, 2025 Initial version.
 */
add_filter( 'tribe_events_get_closest_event', function ( $event, $post_obj, $mode ) {
	global $post;

	// Get the categories of the event.
	$categories = tribe_get_event_cat_ids( $post->ID );

	// Bail if the event has no categories, and show the next event.
	// NOTE, if the next event has a category, then only events in that category will be shown next.
	if ( empty( $categories ) ) {
		return $event;
	}

	if ( $event ) {
		$is_next = false;
		foreach ( $categories as $index => $category_slug ) {
			// If the next/prev event is in one of the categories, set it as next.
			if ( tribe_event_in_category ( $category_slug, $event->ID ) ) {
				$is_next = true;
			}
		}
		
		// If there is no next event set then look for the next.
		if ( ! $is_next ) {
			$find_next_closest_event = new Tribe__Events__Adjacent_Events();
			$find_next_closest_event->set_current_event_id ($event->ID);
			return $find_next_closest_event->get_closest_event($mode);
		}
	}

	return $event;
}, 100, 3 );