您的代码中有一些小错误.

There are some small mistakes in your code.

注意:请注意，如果将新字段添加到注册表单中，***在多个位置返回此字段，以便用户随后进行调整.

NOTE: Be aware that if you add a new field to the registration form, it is best to have this field returned in several places, so that the user can adjust it afterwards.

请参阅: https://businessbloomer.com/woocommerce- add-select-field-account-register-form/

第3部分:显示字段 @用户个人资料(管理员)和我的帐户编辑页面(前端)

Part 3: Display Field @ User Profile (admin) and My Account Edit page (front end)

所以你得到

So you get

/**
 * Add morello account number to reg page
 */
function add_register_form_field() {
    ?>
    <p class="woocommerce-form-row woocommerce-form-row--wide form-row form-row-wide"> 
        <label for="reg_morello_account_number"><?php _e( 'Morello Account Number', 'woocommerce' ); ?> <span class="required">*</span></label> 
        <input type="text" class="woocommerce-Input woocommerce-Input--text input-text" name="morello_account_number" id="reg_morello_account_number" value="<?php if ( ! empty( $_POST['morello_account_number'] ) ) echo esc_attr( $_POST['morello_account_number'] ); ?>" /> 
    </p> 
    <?php
}
add_action( 'woocommerce_register_form', 'add_register_form_field' );

/**
 * Save morello account number
 */
function save_register_fields( $customer_id, $new_customer_data, $password_generated ) {
    if ( isset( $_POST['morello_account_number'] ) ) {
        update_user_meta( $customer_id, 'morello_account_number', wc_clean( $_POST['morello_account_number'] ) );
    }

}
add_action( 'woocommerce_created_customer', 'save_register_fields', 10 , 3 );

/**
 * Add columns
 */
function morello_account_number_column( $columns ) {
    $columns['morello_account_number'] = "morello Account Number";
    return $columns;
}
add_filter('manage_edit-shop_order_columns', 'morello_account_number_column', 10, 1 );

/**
 * Populate columns
 */
function morello_placeholder( $column, $post_id ) {
    // Get order
    $order = wc_get_order( $post_id );

    // Get user id
    $user_id = $order->get_user_id();
    
    if( $column == 'morello_account_number' ) {
        $a_a_n = get_user_meta( $user_id, 'morello_account_number', true );

        // Value is found
        if ( !empty($a_a_n) ) {
            echo $a_a_n;    
        } else {
            echo 'something else';
        }
    }
}
add_filter( 'manage_shop_order_posts_custom_column', 'morello_placeholder', 10, 2 );