help...Sync to iTunes does not work

For eons I have been able to sync my iPhone to iTunes (for backup purposes) with zero issues. For the last 3 months, it has not been working...and I am at a loss. I have an iPhone 8, iOS 12.1. Syncing to an iMac 21.5" running High Sierra 10.13.6. Brand new cable. All I get when I plug the phone into the cable is Photos opening. iTunes does not open (like it used to) and when I open it manually, my iPhone isn't shown anywhere, not under File-> Devices, etc. Something is really amiss with the process now. I have no interest in using iCould to back up the phone. If anyone can help, I would really appreciate it.