USB Keyboard on MAC: \ and < characters inverted
This can be caused when the OS mis-identifies the keyboard. To get that back, clear the preference that saves which device is which layout.

How to reset the mac keyboard

I made as described in the post:


Delete the file /Library/Preferences/com.apple.keyboardtype.plist
Disconnect the keyboard
Reconnect the keyboard
Restart the os


After doing these steps, the keyboard had to be recognized again, and it fixes the issue.

The correct keyboard for Italian is ISO (Eur).