Check if product is in cart

functions.php

<?php
function conditional_checkout_field( $checkout ) {
echo '<div id="conditional_checkout_field">';
 
$check_in_cart = conditional_product_in_cart(xxxx); //replace xxxx with the product id
       
        // Check if the product is in the cart and show the custom fields if it is
        if ($check_in_cart === true ) {
                echo '<h2>'.__('My Custom Checkout Field').'</h2>';
 
                woocommerce_form_field( 'custom_field', array(
                'type'          => 'text',
                'class'         => array('my-field-class form-row-wide'),
                'label'         => __('Label for my Custom Field'),
                'placeholder'   => __('Placeholder to help describe what you are looking for'),
                ), $checkout->get_value( 'custom_field' ));
        }
}
?>