WooCommerce - Automactically Mark Orders as Complete

woo-orders-auto-complete.php

<?php
/**
 * Auto Complete all WooCommerce orders.
 */
function dctit_custom_woocommerce_auto_complete_order( $order_id ) {
    if ( ! $order_id ) {
        return;
    }
 
    $order = wc_get_order( $order_id );
    $order->update_status( 'completed' );
}
add_action( 'woocommerce_thankyou', 'dctit_custom_woocommerce_auto_complete_order' );