The FBI proposed that Apple could write a new operating system variant that would let the FBI robot-brute-force the password, for certain older models at the ti

The FBI proposed that Apple could write a new operating system variant that would let the FBI robot-brute-force the password, for certain older models at the time (without a Secure Enclave). I believe Apple changed how operating system updates were installed after this point so that they did not have the capability to upgrade the phone's operating system without access to the device passcode.