Can't sync iPhone in iTunes anymore
iMac Mid 2011 running High Sierra Version 10.13.6
iTunes for Mac Version 12.8.3.1
iPhone 8 on IOS 14.5.1
When connecting my iPhone i get the message "A software update is required to connect to your iPhone" or words to that effect. I click Continue and a popup appears "Downloading 1 item" this stays for a good few minutes but then eventually, after about 20 minutes or so, fails with an error "Installation failed. Can't download the software because of a network problem."
Incidentally the same thing happens with my iPad Pro running IOS 14.4.2 only the first message is along the lines of "A software update is required to update your iPad". Both of them fail with the same network error when trying to download, what im assuming is an iTunes update?
My network is fine, im connected via Ethernet not Wi-Fi so there's no interruption to the internet. I've tried several times a day, at different times of day for about the past week and get the same error every time. When looking at Activity Monitor there are next to no packets coming in during this alleged download, 40 ish packets per second, data received about 8KB/s so there's clearly nothing downloading.
iMac 27″, macOS 10.13