The qty_in_cart property is removed from the Stencil Common Product Card object
As part of an effort to improve the performance of BigCommerce storefronts, the
qty_in_cart property is no longer supported on the Stencil Common Product Card Model. This property will return 0 from now on, and its use is discouraged.
The Storefront Cart API can be used instead to get details of products in the cart.