Apple tries to address AirTag unwanted tracking issues in updated safety document.
Both AirTag and the Find My network are designed with privacy at their core. AirTag and Find My network accessories have unique Bluetooth identifiers that change frequently. To discourage unwanted tracking, Find My notifies you if an unknown AirTag or other Find My accessory is seen moving with you over time by sending you the message, “Item Detected Near You.” (This feature is available on iPhone, iPad, or iPod touch running iOS 14.5 or iPadOS 14.5 or later). If you see this message on your device, an AirTag or other Find My accessory that has been separated from the person who registered it is traveling with you, and the owner might be able to see its location. It’s possible that the AirTag might be attached to an item you are borrowing.Apple
Apple: Personal Safety User Guide