OK, I’ve had a chance to find the appropriate installers and tried them out. My setup is very close to yours with a 16GB iMac18,3 macOS 10.14.6 (18G6032), iTunes 12.9.5.5, but iPhone 7 with iOS 14.0.1.
- Make a backup first!
- Download then double click the Mobile Device Bundle installer package http://swcdn.apple.com/content/downloads/53/42/001-48233-A_WV9MCDEX38/hqv80f2pb0e1b4314wgnzcmfor0nidd8h1/CoreTypes.pkg
- Download then double click the Mobile Device On Demand installer package http://swcdn.apple.com/content/downloads/53/42/001-48233-A_WV9MCDEX38/hqv80f2pb0e1b4314wgnzcmfor0nidd8h1/MobileDeviceOnDemand.pkg
You might need to cut and paste these links in a new browser tab
You’ll need your admin password for each installation
Each installation requires additional time to run scripts and optimize the OS.
I had previously installed this update on my Mac, but with the issues surrounding Safari 14 I had reverted back to macOS 10.14.6 reinstall, Safari 13 and Security Update 2020-004, so can’t be positive that it was still there before accomplishing the above.
Had no problem connecting the iPhone to the iMac after.
Good Luck
-Al-