iOS 12 compatibility with iTunes running on OS yosemite 10.10.4

I have this problem too as I can't upgrade my OS past El Capitan without paying the same amount for upgrades to my audio software.

First I went to the apple store and someone there suggested I sync wirelessly with iTunes. This only works if you subscribe to Apple Music or another service they provide, which in my case is a rip off but that may work for you. And they have limitations - if it's not purchased music then it's uploaded to your iCloud and they let you stream it from your iCloud. So that was not an option for me. Simply because not being able to plug my iPhone in and use my iTunes as normal is BS, and I'm not connected to the internet for streaming where I work.

However, using an external drive you can install the latest OS or a compatible OS with a compatible iTunes onto the drive. When you want to manage your music, boot to that drive on startup and run iTunes. You don't have to erase or reboot your actual computer from a backup this way and it only costs what an external drive with sufficient space costs.

For me since I have a lot of music, it works to my advantage as I have more space on my computer. It still ***** and I'll never buy an apple computer or phone again after this and other experiences regarding this. But it's not near the cost of a new computer.

Actually hey sorry - I thought the drive would work but not exactly. When I plugged my phone in again while booted from my ecternal drive a message appeared to update software. Before I was afraid it would update my OS on my mac which was not what I wanted at all. But it only updated either something in the phone or something in iTunes. I can use it just fine now and didn't have to change OS.