Under GDPR consent can’t be “freely given” when it’s bundled as a condition of service unless the consent they’re asking for is necessary in order to perform the service. To use your example:

The grocery store doesn’t need to ask if you consent to paying for an apple because if you didn’t consent there wouldn’t be any transaction to perform.

Now if you paid for your apple and the cashier said okay hand over your phone so I can poke around a bit because there’s some fine print that says by nature of walking through the front doors you agree to allow the store to look through your phone. Did you consent to that? Of course not.

Consent wasn’t “freely given” because the store is requiring you disclose information (the contents of your phone) as a condition of service (you can’t even walk through the door without “consenting” let alone make a purchase) and that information isn’t necessary in order for the store to complete the transaction.

GDPR says they have to ask you first (usually in the form of a giant irritating banner as soon as you walk in the door) and that if you say no they have to let you buy your apple anyway.