Troubleshoot iTunes Application in Mac
There are cases in which you might find the iPhone is unavailable to be recognized on your Mac system.
Check for the following options in order to resolve the connection error.
Check the USB port in your Mac, the USB cable, and the port on our iPhone.
If you have any dust accumulated inside the ports, blow air inside the ports to clear out the dust.
Connect the iPhone to the Mac to see if the problem iPhone not connecting to mac still persists.
Try using a different USB cable if possible.
Make sure you have tapped the option Trust the device when the message is prompted, this will allow the full access of the iPhone device to the computer.
Restart both the Mac system and the iPhone device.
Make sure you have the latest version — the Mac OS Catalina — installed on your Mac to resolve the unknown error.
Update the version of iOS on your mobile device, and the latest version is iOS 13.
Make sure you turn off any third-party applications installed on your Mac.
The antivirus applications will cause disruptions and might also be a cause of the iPhone not connecting to mac computer.