Adds a new action button on the WooCommerce order list to view the thank you page for each order.

woo-thankyou-page-action.php

<?php 

// 	Add a new action button for the thank you page for each order
// 	WooCommerce version 3.3+

add_action( 'woocommerce_admin_order_actions_end', 'add_thankyou_page_action_button', 100, 1 );
function add_thankyou_page_action_button( $order ) {

    // Add more order status here
    if ( $order->has_status( array( 'processing', 'completed', 'partial-comp' ) ) ) {

    $order_id = method_exists($order, 'get_id') ? $order->get_id() : $order->id;
    $order_key = $order->get_order_key();

    $url    = esc_url(home_url().'/checkout/order-received/'.$order_id.'/?key='.$order_key);
    $name   = esc_attr( __('Thank You Page', 'woocommerce' ) );
    $class  = esc_attr( 'thankyou-page' );

    // Custom action button (with a target='_blank' opening a new browser window)
    printf( '<a class="button wc-action-button wc-action-button-%s %s" href="%s" title="%s" target="_blank">%s</a>', $class, $class, $url, $name, $name );

    }
}

// The icon of your action button (CSS)
add_action( 'admin_head', 'add_thankyou_page_action_button_css' );
function add_thankyou_page_action_button_css() {
    echo '<style>.wc-action-button-thankyou-page::after { font-family: woocommerce !important; content: "\e028" !important; }</style>';
}

?>