The function is for change order status to competed if order is virtual and downloadable

woocommerce_payment_complete_order_status.php

<?php
add_filter( 'woocommerce_payment_complete_order_status', 'virtual_order_payment_complete_order_status', 10, 4 );
/*
* move processing to completed
*/
function virtual_order_payment_complete_order_status( $order_status, $order_id ) {
	$order = wc_get_order( $order_id );
	
	if ( 'processing' == $order_status ) {			
		$virtual_order = null;			
		if ( count( $order->get_items() ) > 0 ) {			
			foreach( $order->get_items() as $item ) {					
				if ( 'line_item' == $item['type'] ) {						
					$_product = $order->get_product_from_item( $item );						
					if ( $_product->is_virtual() && $product->is_downloadable()) {
						// once we've found one non-virtual product we know we're done, break out of the loop
						$virtual_order = true;												
					} else {
						$virtual_order = false;
						break;	
					}
				}
			}
		}
		
		// virtual order, mark as completed
		if ( $virtual_order ) {
			return 'custom-completed';
		}
	}

	// non-virtual order, return original status
	return $order_status;
}