Send default WooCommerce email when switching from custom order status

Looks like I was overcomplicating things. This is the solution:

add_filter( 'woocommerce_email_classes', 'custom_woocommerce_email_classes', 10, 1 );
function custom_woocommerce_email_classes( $email_classes ) {
    $email_classes[ 'WC_Email_Customer_On_Review_Request' ] = include_once 'includes/classes/class-wc-email-customer-on-review-request.php';

    // Register custom trigger to send on-hold email when status is switched from on-review to on-hold.
    add_action( 'woocommerce_order_status_on-review_to_on-hold_notification', [
        $email_classes[ 'WC_Email_Customer_On_Hold_Order' ], 'trigger'
    ], 10, 2 );

    return $email_classes;
}