How can I transfer my Apple Gift Card balance to my bank account?

No, you cannot buy groceries.

Apple gift cards are for the purchase of Apple products and services. Please review the information in the Apple Support article I linked to below.

What you can buy with your Apple Gift Card or Apple Account balance - Apple Support

We need to know exactly what card you're referring to. If it's an Apple Gift Card, then as you've already been told, it only works in Apple's stores (Apple Store, App Store, iTunes Store, etc). You cannot use it with any other store or company.

You can’t. Apple Gift cards, like gift cards from any store, are non-transferable and non-refundable. Sorry.

Apple Card is a credit card. Do you have a credit card and not an Apple Gift Card?

Apple Cash is a prepaid debit card only available in the US. Did you apply for an Apple Cash account or purchase a gift card?

Apple Gift cards are purchased in stores. Did you purchase your cards in a store?