Order fields on printed order

I have added a comment field according to the steps at the project page. And that field is indeed displayed when viewing the order. Nice!
But I also want to have that comment field on the printed order.
I use entity_print for that. So the template for the printed order is commerce-order-receipt--entity-print.html.twig.
No I struggle to get the preprocess function to get the order field in that template.
Can one perhaps provide an example?