@James Tompkins, it lets you type the password, it's just NOT shown to you as a security measure. Just type your password completely and press enter

Sometimes, the issue is purely a software one. Occasionally, there are problems with usbd daemon programme, which is the root of the issue with the iPhone. A possible solution to this problem is to open Terminal.app (Applications -> Utilities -> Terminal) and execute the following command: sudo killall usbd . It will kill the programme and it will immediately relaunch. You will need to provide your password. Please note that the password will not be visible, it is normal. If it does not work, try entering a different command in Terminal: sudo killall -STOP -c usbd . Once more, you may need to present your password