Adding term to a custom taxonomy based on term from product category

As you say, when triggered ‘save_post’ the changes are not been mae, so there’s not yet an association with a term.

But..in the $_POST['product_cat'] variable you have the array (IDS) of the selected categories, so you can check if the product belongs to the ‘Keyboard’ category ( based on its ID) and decide whether or not to perform further actions