WordPress: Add custom post types into the feed.

add-post-type-to-feed.php

<?php
/**
 * Add Custom Post Types (CPT) to feeds
 * 
 * @todo Change the `prefix_` and with your own unique prefix.
 * 
 * @since 1.0.0
 * 
 * @return object
 */
if( ! function_exists( 'prefix_add_custom_post_types_to_feed' ) ) :
	function prefix_add_custom_post_types_to_feed( $query ) {

		// Is feed then add custom post types.
		if ( is_feed() ) {
			$query->set( 'post_type', array( 'post', 'astra-portfolio', 'deal' ) );
		}

		return $query;
	}
	add_filter( 'pre_get_posts', 'prefix_add_custom_post_types_to_feed' );
endif;