How can I prevent a product from displaying the 'Add to cart' button?

If you want to prevent a certain product from displaying the app widget, just add the tag   cbb-avoid-add-to-cart-button to that product from the products section of your Shopify admin zone, as explained at the end of the Location preferences section:

If you want to prevent a certain collection from displaying the app widgets, you can add the tag cbb-avoid-add-to-cart-button to all the products of the collection.

Please note that it may take a few minutes for Shopify to make these changes effective. You can watch this Shopify video (starting on minute 7:00) to learn how to add new tags to products.