"Automatically sync when this iPhone is connected" is grayed out

As far as the Auto sync, instead of making that change in the Summary Page, go to Edit>Preferences>Devices, and check if the circled box is checked. That will make a difference. If it was, then uncheck it, close iTunes and then open it again.

Are you using either of Apple Music or iTunes Match?

Is your device set up for manual management?

Is the Prevent iPods, iPhones, and iPads from syncing automatically option selected?

Assuming the answer to all three is no, try Re: iTunes won't reopen after I close it.

tt2

I faced this issue with two iPhones on two Windows computers. Downloading iTunes from the Microsoft Store does not also include the secondary programs (Bonjour, Apple Mobile Device Support, etc.) that allows this functionality--permitting the automatic syncing of iPhone and iTunes when the phone is plugged in. The checkbox for this option in the Summary choice of the iPhone mode is grayed out and unavailable.

Here is a workaround:

Uninstall the Microsoft acquired version of iTunes and install an archival version (the October 2018 version(s) of iTunes from Apple...

Troubleshooting issues with iTunes for Wi… - Apple Community

I spent many, many hours on the phone with Apple tech support. They claim to be vaguely aware of this problem which one would assume affects hundredsif not thousands of iPhone/Windows users. Why Apple and Microsoft have made it their policy to reduce the functionality of their products is beyond me. I hope this workaround works for you.

If you're using Apple Music then you will have likely enabled iCloud Music Library on the device. In this case changes you make to the library on your device or your computer are mirrored to the other over Wi-Fi, so music syncing is disabled.

The post of mine that I linked to is concerned with resolving odd settings issues in iTunes where controls are mysteriously disabled, or reset each time you start iTunes.

tt2

Weird, I could have sworn I was replying to a different thread... Ignore the previous version of this post.

In principle the Microsoft Store version should include all of the software required for iTunes to work with your devices, but is installed as one package rather than a suite. I suspect in practice a combination of security settings and perhaps legacy registry information means that the Microsoft Store version doesn't seem to work perfectly for everyone.

tt2

Settings > Music > iCloud Music Library.

tt2

So perhaps we're back to odd settings issues after all. 😕

tt2

I had the same problem after the latest update. I uninstalled itunes, then downloaded & reinstalled it. All my music & playlists are still intact.

Thank you so much for sharing, I was going crazy wondering wth was the problem, but this fixed it!