Suddenly iTunes sync button greyed out
I added some albums to my library in iTunes for Windows and went to sync them to my iPhone 14 Pro but the sync button is grey and can't be pushed. I'm using 12.12.9.4. I tried re-installing iTunes with no luck, then I uninstalled and tried the preview versions from the Microsoft Store but had no better results. I also tried doing this with my new work MacBook Pro but get the same problem there. I've been adding music to sync to my library for many years and have never seen this before.
iPhone 14 Pro