You can try out this module:
it adds many options to sort products in toolbar, still if you want to have custom sorting then simply can download this one and get an idea of code to be written.
You are so closed on finding out the answer on yourself.
If you dig further, you will find the item renderer uses item template vendor/magento/module-sales/view/frontend/templates/email/items/order/default.phtml
You can just override this template and remove the option display from line 19-28
Or with a better DI plugin approach, create a afterGetItemOptions ...