What personal data is sent when paying?

Apple only receives encrypted data and does not have the key to decrypt the data. Unless Apple is the merchant, and then they receive shipping address (likely on file) and the details necessary to fulfill the order. The supermarket already knows what you’re purchasing and will do whatever is required to meet federal and state requirements. Apple can’t supply the notification you’d like, because they do not know what you’re purchasing if they are not the merchant, because the data is encrypted. Merchants have their own privacy policies in regard to how they handle the data they receive.

The request would be if it’s an order being shipped. Normally, address, phone number and email would not be provided to the merchant. However, if the purchaser requests/requires shipment, Apple Pay must provide address, email and phone number so merchant can contact purchaser if there is a delay in shipment or delivery etc.

Customer name and partial card details, depending on the type of purchase and the type of business. Some businesses are required to have additional information, such as purchase of firearms, some prescriptions, etc. If the purchase is for shipping, name, address, email and/or phone number to contact the purchaser.

Not sure what silent supermarket checkout profiling is. My experience is more on the financial side.

The information being shared was already entered by the account holder or authorized user in their iPhone at this path,

iPhone > Settings > Wallet &Apple Pay > Transaction Defaults > this information includes name, address, email and phone number.

That’s what happens, as best as I can confirm. I have a merchant account and I accept Apple Pay. I know the data I get when I do a transaction and when I accept an order for shipment.