Can I stop customers from buying the gift product on its own? (Essential Free Gift BOGO BXGY app)

There's no built-in "gift only" option. The gift is a normal product in your store, and its title and image in the widget link to its product page.

To make it less visible:

• Leave the product out of your menus and collections.
• Keep it available on the Online Store sales channel, because the app needs that to add it to the cart.

Customers who find the product page can still buy it. If you need a gift-only product, let us know and we'll add your vote to the feature request.