My wife upgraded from what I believe was an iPhone 11 to an iPhone 14 Pro and chose to have the data transferred in the store. The employee said using a Mac would make the transfer faster because it was taking a long time. This happened in the middle of the store during a busy period, with plenty of people around. I assumed the phones would be connected directly, so I've been wondering ever since whether using a store Mac was normal or whether I'm being unnecessarily paranoid.
2 Answers
The usual fast method is to connect the two iPhones directly with a cable and use the phone-to-phone transfer process. A Mac might have been used to update iOS or troubleshoot the transfer, but backing up a customer’s phone to a shared store computer would not be a normal or appropriate procedure.
It’s unlikely the employee intentionally copied all the data onto a shared Mac, especially in the middle of a busy store. The computer may have been used to help with an update or setup issue. Still, staff generally should not create a customer backup on a shared machine, since that could leave personal data behind.
The fact that it happened in a public area is somewhat reassuring, but the proper approach would still be a direct cable transfer or a cloud backup controlled by the customer.

That makes sense. I mainly worried that the phone’s contents might have been copied onto the computer rather than transferred directly between the devices.