Different recipients based on product category in WooCommerce email notification

The following will add additional recipients to "New Order" email notification based on your product categories, that you will define in an indexed array with an email recipient / product category pairs:

add_filter( 'woocommerce_email_recipient_new_order', 'custom_email_recipient_new_order', 10, 2 );function custom_email_recipient_new_order( $recipient, $order ) {    // Not in backend when using $order (avoiding an error)    if( ! is_a($order, 'WC_Order') ) return $recipient;    // Define the email recipients / categories pairs in the array    $recipients_categories = array(        'email.one@email.com'   => 'category-one',        'email.two@email.com'   => 'category-two',        'email.three@email.com' => 'category-three',    );    // Loop through order items    foreach ( $order->get_items() as $item ) {        // Loop through defined product categories        foreach ( $recipients_categories as $email => $category ) {            if( has_term( $category, 'product_cat', $item->get_product_id() ) && strpos($recipient, $email) === false ) {                $recipient .= ',' . $email;            }        }    }    return $recipient;}

Code goes in functions.php file of your active child theme (or active theme). Tested and works.

Notes:

• The defined Product categories can be term Ids, term slugs or term names.
• Each product category need to be defined in the related products as has_term() WordPress conditional function doesn't handle parent terms.

###Addition to handle parent product categories:

// Custom conditional function that handle parent product categories toofunction has_product_categories( $categories, $product_id = 0 ) {    $parent_term_ids = $categories_ids = array(); // Initializing    $taxonomy        = 'product_cat';    $product_id      = $product_id == 0 ? get_the_id() : $product_id;    if( is_string( $categories ) ) {        $categories = (array) $categories; // Convert string to array    }    // Convert categories term names and slugs to categories term ids    foreach ( $categories as $category ){        $result = (array) term_exists( $category, $taxonomy );        if ( ! empty( $result ) ) {            $categories_ids[] = reset($result);        }    }    // Loop through the current product category terms to get only parent main category term    foreach( get_the_terms( $product_id, $taxonomy ) as $term ){        if( $term->parent > 0 ){            $parent_term_ids[] = $term->parent; // Set the parent product category            $parent_term_ids[] = $term->term_id; // (and the child)        } else {            $parent_term_ids[] = $term->term_id; // It is the Main category term and we set it.        }    }    return array_intersect( $categories_ids, array_unique($parent_term_ids) ) ? true : false;}// Adding custom recipients based on product categoriesadd_filter( 'woocommerce_email_recipient_new_order', 'custom_email_recipient_new_order', 10, 2 );function custom_email_recipient_new_order( $recipient, $order ) {    // Not in backend when using $order (avoiding an error)    if( ! is_a($order, 'WC_Order') ) return $recipient;    // Define the email recipients / categories pairs in the array    $recipients_categories = array(        'email.one@email.com'   => 'category-one',        'email.two@email.com'   => 'category-two',        'email.three@email.com' => 'category-three',    );    // Loop through order items    foreach ( $order->get_items() as $item ) {        // Loop through defined product categories        foreach ( $recipients_categories as $email => $category ) {            if( has_product_categories( $item->get_product_id(), array( $category ) ) && strpos($recipient, $email) === false ) {                $recipient .= ',' . $email;            }        }    }    return $recipient;}

Code goes in functions.php file of your active child theme (or active theme). Tested and works.

Note: The Product categories can be term Ids, term slugs or term names.

Similar: Different recipients based on products sold in WooCommerce email notification