My iPhone is an iPhone 7 using iOS 12, and my iPod touch is a 5th generation running iOS 9. Do I still need the Mobile Device Update? Sounded like it was needed for newer hardware (maybe).No, it should be working. Just a few days ago I made backups for an iPhone 11 Pro Max and an iPhone XS Max using iTunes 22.214.171.124 on Mojave 10.14.6 (18G2022). Be sure to install the Mobile Device update, see https://forums.macrumors.com/threads/sync-itunes-on-iphone-7-and-ios-13-2-with-imac-and-mojave-10-14-6.2209537/
I should also mention that I did not install iTunes 12.6.5 using the above procedure. I did it by using a script you provided on the iTunes 12.6.5 for Catalina thread, in response to someone who asked you "do you have a script for Mojave". I then had no luck in getting iTunes to launch until I remember the part about iPod framework and copied that into the newer iTunes.
I did all of the above with SIP disabled. As per your recommendations, I also installed iTunesAccess.pkg, , using a link you provide, which I do not know the function of.
I should also mention that I did ONE sync with iTunes 12.6.5 (my first one) when I could see my previous backups and the backup was successful. But immediately after that was completed, I have since lost the ability to either see the old backups or do a successful backup. It almost looks like a permissions issue, as if iTunes 12.6 isn't allowed to see the contents of the folder where the backups are.
I suspect I should perhaps trash the iTunes 12.6.5 I installed and start again from scratch using the method on this page.