iPhone 14 won't connect to Mac

My iphone 14 has suddenly decided it won't connect to my Mac so that I can do back up. The Mac is running OS 10.13 and won't allow me to update any further. Just updated the iPhone to 17.1.1. Itunes no longer wants to even show the iphone on the screen. However, when I plug in the phone to the Mac, the photos gallery comes up and it charges. Just won't do a backup.