How do I downgrade my iTunes

I can no longer sync my iPhone to my Mac using a USB cable. iTunes says I need to update my OS but I cannot because of the age of my Mac Pro (Early 2009, OS 10.13.6). My iTunes is version 12.8.2.3

I want to downgrade my iTunes back to a version that will allow SUB syncing.

Any help? Suggestions? I currently am using Sync over WiFi but I have a LARGE music library on my phone and it takes forever...

TIA

Lee