This is quite an issue I also had for iOS 17 as well, but I accidentally ended the process though and I had to wait till iOS 17 was released.
This year with iOS 18, I get the same issue except I did actually download it. It installed and went through as it prompt me to close iTunes before installing it. However, as I open iTunes after it was installed, my hopes weren’t up at all and it gave me another prompt to download it again. The prompt that was given to me is:
A software update is required to connect to iPhone.
I clicked install and waited for the process to download. However it never did download for some reason, and as I thought it was working, few minutes goes by and I get a new message saying:
Installation Failed: Can’t install the software because it is not currently available from the Software Update server.
So what now? This also occurs with public beta and developer beta. I know there’s such thing as a mobile framework for it to work but how do I get it to work on iTunes? I’m running High Sierra by the way. Does anyone have a solution to this? I have a backup of my iPhone via iTunes made before I download it in case if I have to downgrade it but it won’t be possible if iTunes won’t recognize my iPhone.