I am trying to Factory Restore iPhone 6S "A1633" on my Mac Running Big Sur 11.1 / Intel.
I am in recovery mode on the phone and plug it in it starts the update OR restore downloads the file, installs then produces this error. It seems that the firmware file from apple is corrupt in some way.
The iPhone “iPhone” could not be restored because the firmware file was corrupt.
Disconnect and reconnect, then try again.