A quick proof of concept of using an order ID to generate a CSV of order details.

wc-export-order-csv.php

<?php
/*
Plugin Name: WooCommerce - Export order details as CSV
Plugin URI: https://www.damiencarbery.com/
Description: Allow exporting the details .
Author: Damien Carbery
Author URI: https://www.damiencarbery.com
Version: 0.1
*/

/*
https://stackoverflow.com/questions/4545311/download-a-file-by-jquery-ajax
https://codepen.io/chrisdpratt/pen/RKxJNo

https://stackoverflow.com/questions/4545311/download-a-file-by-jquery-ajax
*/

//add_action( 'wp_ajax_nopriv_ajax_code_generator_name', 'ajax_export_order_csv_func' );
add_action( 'wp_ajax_export_order_csv', 'ajax_export_order_csv_func' );


add_filter( 'woocommerce_order_item_add_action_buttons', 'dcwd_add_export_order_csv_button' );
function dcwd_add_export_order_csv_button( $order ) {
	//error_log( 'Order ID: : ' . $email_heading );
	//printf( '<a href="?order_id=%d">Export CSV</a>', $order->get_id() );
	printf( '<button type="button" class="button export-csv">%s</button>', esc_html( 'Export CSV (ajax)', 'woocommerce' ) );
	printf( '<a href="%s%d"><button type="button" class="button export-csv-link">%s</button></a>', 'http://localhost/woo-hpos/wp-json/export-order-csv/v1/export-order-csv/', $order->get_id(), esc_html( 'Export CSV (REST API)', 'woocommerce' ) );

	add_action( 'admin_footer', 'dcwd_add_export_order_csv_js' );
}


function get_order_data_as_csv( $order_id ) {
	$order_csv = array();

	$order = wc_get_order( $order_id );
	if ( $order ) {

		// Add billing details on separate lines (each line is an array [within an array]).
		$order_csv[] = array( $order->get_billing_first_name(), $order->get_billing_last_name() );
		$line = $order->get_billing_company();
		if ( ! empty( $line ) ) {
			$order_csv[] = array( $line );
		}
		$order_csv[] = array( $order->get_billing_address_1() );
		$line = $order->get_billing_address_2();
		if ( ! empty( $line ) ) {
			$order_csv[] = array( $line );
		}
		$order_csv[] = array( $order->get_billing_city() );
		// Get full state name instead of abbreviation.
		$order_csv[] = array( WC()->countries->states[ $order->get_billing_country() ][ $order->get_billing_state() ] );
		$order_csv[] = array( $order->get_billing_postcode() );
		// Get full country name instead of abbreviation.
		$order_csv[] = array( WC()->countries->countries[ $order->get_billing_country() ] );
		$order_csv[] = array( $order->get_billing_email() );
		$order_csv[] = array( $order->get_billing_phone() );
		
		$order_csv[] = array();  // Add empty line before the items.

		// Add product name and quantity on same line (stored as an array).
		foreach ( $order->get_items() as $item_id => $item ) {
			//$product_id = $item->get_product_id();
			//$variation_id = $item->get_variation_id();
			//$product = $item->get_product(); // see link above to get $product info
			$product_name = $item->get_name();
			$quantity = $item->get_quantity();
			//$subtotal = $item->get_subtotal();
			//$total = $item->get_total();
			//$tax = $item->get_subtotal_tax();
			//$tax_class = $item->get_tax_class();
			//$tax_status = $item->get_tax_status();
			//$allmeta = $item->get_meta_data();
			//$somemeta = $item->get_meta( '_whatever', true );
			//$item_type = $item->get_type(); // e.g. "line_item", "fee"

			$order_csv[] = array( $product_name, $quantity );
		}
	}

	return $order_csv;
}

function ajax_export_order_csv_func() {
	//error_log( 'In ajax_export_order_csv_func().' );
	//error_log( '$_POST: ' . var_export( $_POST, true ) );

	if ( ! current_user_can( 'edit_shop_orders' ) ) {
		wp_die( -1 );
	}


	$order_id = intval( $_POST[ 'order_id' ] );
	$order_data = get_order_data_as_csv( $order_id );
    // Open raw memory as file, no need for temp files.
    $f = fopen( 'php://memory', 'w' );
    // loop through array
    foreach ($order_data as $line) {
        // default php csv handler
        fputcsv( $f, $line );
    }
    // Rewrind the "file" with the csv lines
    fseek($f, 0);

	header('Content-Description: File Transfer');
    // Modify header to be downloadable csv file
    header('Content-Type: text/csv');
    header('Content-Disposition: attachment; filename=order-' . $order_id . '.csv');

    // Send file to browser for download
    fpassthru($f);

//	wp_send_json_error();
	wp_die();
}


function dcwd_add_export_order_csv_js() {
?>
<script>
jQuery(document).ready( function( $ ) {
    jQuery( '.export-csv' ).on( 'click', function(e) {
		//alert( 'Export CSV button clicked.' );
        e.preventDefault();
		jQuery.ajax({
            url : '<?php echo admin_url( 'admin-ajax.php' ); ?>',
            type : 'post',
/*xhrFields: {
	responseType: 'blob'
},*/
           data : {
                action : 'export_order_csv',  // Note that this is part of the add_action() call.
				order_id: woocommerce_admin_meta_boxes.post_id,
// ToDo: Add nonce, maybe one on the same page.
                //submitted_nonce : " . $ajax_js_object_name . ".the_nonce,
            },
            success : function( data ) {
				var uri = 'data:application/csv;charset=UTF-8,' + encodeURIComponent(data);
				location.href = uri;
/*var disposition = response.getResponseHeader('Content-Disposition');
console.log( 'disposition:', disposition );
        var matches = /"([^"]*)"/.exec(disposition);
console.log( 'matches:', matches );
        var filename = (matches != null && matches[1] ? matches[1] : 'order-export.csv');
console.log( 'filename:', filename );

var blob = new Blob([response.response], { type: 'text/csv' });
        var link = document.createElement('a');
        link.href = window.URL.createObjectURL(blob);
        link.download = filename;

        document.body.appendChild(link);

        link.click();

        document.body.removeChild(link);
*/
			},
            error : function( response ) {
                alert('Error retrieving the information: ' + response.status + ' ' + response.statusText);
                console.log( response );
            }
        });
    });
});
</script>
<?php
}


class ExportOrderCSVServer extends WP_REST_Controller {
	private $api_namespace;
	private $base;
	private $api_version;
	private $required_capability;

	
	public function __construct() {
		$this->api_namespace = 'export-order-csv/v';
		$this->base = 'export-order-csv';
		$this->api_version = '1';
		$this->required_capability = 'read';  // Minimum capability to use the endpoint
		
		$this->init();
	}
	
	
	public function register_routes() {
		$namespace = $this->api_namespace . $this->api_version;
		
		register_rest_route( $namespace, '/' . $this->base . '/(?P<id>[\d]+)', array(
			array( 'methods' => WP_REST_Server::READABLE, 'callback' => array( $this, 'generate_order_csv' ),
			'args' => array( 'id' => array( 'validate_callback' => function($param, $request, $key) { return is_numeric( $param ); } ), ),
			'permission_callback' => '__return_true' ),
		)  );
	}


	// Register our REST Server
	public function init(){
		add_action( 'rest_api_init', array( $this, 'register_routes' ) );
	}


	// From: https://stackoverflow.com/a/70008574/8605943
	public function generate_order_csv( WP_REST_Request $request ) {
		$response = new WP_REST_Response;
		$order_id = (int) $request['id'];
        $response->set_data( $order_id );
        $response->set_headers( [
            'Content-Type'   => 'text/csv',
            //'Content-Length' => filesize( $path ),
			'Content-Disposition' => 'attachment; filename=order-' . $order_id . '.csv',
        ] );

//error_log( 'Set order id to ' . $request['id'] );
        // HERE → This filter will return the CSV content.
        add_filter( 'rest_pre_serve_request', array( $this, 'generate_csv_data' ), 0, 4 );
		
		return $response;

	}


	// ToDo: Get more info from _oembed_rest_pre_serve_request() in wp-includes/embed.php
	public function generate_csv_data( $served, $result, $request, $server ) {
		$is_csv   = false;
		$order_id = null;

		// Check the "Content-Type" header to confirm that we
		// really want to return CSV data.
		foreach ( $result->get_headers() as $header => $value ) {
			if ( 'content-type' === strtolower( $header ) ) {
				$is_csv = ( 0 === strpos( $value, 'text/csv' ) );
				$order_id = intval( $result->get_data() );
				break;
			}
		}

		// Create the CSV output and tell the REST server to not send any other
		// details (via "return true").
		if ( $is_csv && is_int( $order_id ) ) {
			// ToDo: Generate CSV data here or earlier.
			$order_data = get_order_data_as_csv( $order_id );

			// Open raw memory as file, no need for temp files.
			$f = fopen( 'php://memory', 'w' );
			// loop through array
			foreach ($order_data as $line) {
				// default php csv handler
				fputcsv( $f, $line );
			}
			// Rewrind the "file" with the csv lines
			fseek($f, 0);


			// Send file to browser for download
			fpassthru($f);

			return true;
		}

		return $served;
	}
}

$export_order_csv = new ExportOrderCSVServer();

woo-get-order.php

<?php
define( 'WP_USE_THEMES', false );
require_once( './wp-load.php' ); 


$order_id = 81;

$order = wc_get_order( $order_id );
if ( $order ) {
	$order_csv = array();

	// Add billing details on separate lines (each line is an array [within an array]).
	$order_csv[] = array( $order->get_billing_first_name(), $order->get_billing_last_name() );
	$line = $order->get_billing_company();
	if ( ! empty( $line ) ) {
		$order_csv[] = array( $line );
	}
	$order_csv[] = array( $order->get_billing_address_1() );
	$line = $order->get_billing_address_2();
	if ( ! empty( $line ) ) {
		$order_csv[] = array( $line );
	}
	$order_csv[] = array( $order->get_billing_city() );
	// Get full state name instead of abbreviation.
	$order_csv[] = array( WC()->countries->states[ $order->get_billing_country() ][ $order->get_billing_state() ] );
	$order_csv[] = array( $order->get_billing_postcode() );
	// Get full country name instead of abbreviation.
	$order_csv[] = array( WC()->countries->countries[ $order->get_billing_country() ] );
	$order_csv[] = array( $order->get_billing_email() );
	$order_csv[] = array( $order->get_billing_phone() );
	
	$order_csv[] = array();  // Add empty line before the items.

	// Add product name and quantity on same line (stored as an array).
	foreach ( $order->get_items() as $item_id => $item ) {
		//$product_id = $item->get_product_id();
		//$variation_id = $item->get_variation_id();
		//$product = $item->get_product(); // see link above to get $product info
		$product_name = $item->get_name();
		$quantity = $item->get_quantity();
		//$subtotal = $item->get_subtotal();
		//$total = $item->get_total();
		//$tax = $item->get_subtotal_tax();
		//$tax_class = $item->get_tax_class();
		//$tax_status = $item->get_tax_status();
		//$allmeta = $item->get_meta_data();
		//$somemeta = $item->get_meta( '_whatever', true );
		//$item_type = $item->get_type(); // e.g. "line_item", "fee"

		$order_csv[] = array( $product_name, $quantity );
	}

	echo '<p>This is the CSV that will be generated (items with spaces are wrapped in quotes):';
	echo '<pre>';
	$out = fopen( 'php://output', 'w' );
	foreach ( $order_csv as $line ) {
		fputcsv( $out, $line );
	}
	fclose( $out );
	echo '</pre>';
}
else {
	echo '<p>Error: Invalid order ID.</p>';
}