Control which Paid WooCommerce Orders are Automatically Completed. WooCommerce automatically completes orders for virtual-downloadable products after successful payment, but it won’t autocomplete other orders, as you may need to take actions between when the order is processed and completed. If you sell shippable products, you probably need to ship them before completing the order. If you sell virtual products like services, you probably have to do something between when the order is paid and completed. However, this isn’t the case for all stores, and you may not need to take any action between when an order is paid for and completed. For example, you may want to auto-complete virtual orders, or even those with products that aren’t virtual or downloadable. Likewise, you may not want any orders to automatically complete at all.
WooCommerce - Order Status Control v1.12.0