I don't think AirTag work that way. AirTag protocol is specifically designed so Apple or other parties will not be able to track users by serial numbers.
Where there's a will, there's a way. Apple is very clear law enforcement can approach them with any AirTag and they will immediately be able to tie it to a user.
They do, Airtag hardware need to be signed to add to your iCloud account. But the actual location beacon messages are not linked to your iCloud account and can’t be associated with the sending airtag.
