How to not display the subscription form for certain products ?

Hello,
First of all, thank you for this simple and well-made plugin.
I have a special request that is not really a support question.
For a website I need to hide this form for products that are out of stock but that will never be in stock again (discontinued products).
The discontinued info is stored in a custom field (ACF).
Is there a hook that I can write in my functions.php file to unset the form if certain conditions are met?
Thanks.