iTunes cannot sync photos to the iPhone “x iPhone” because your Photos Library is not yet available. Please try again later.

You may need to Designate a System Photo Library in Photos - Apple Support.

tt2

I get the same error - itunes cannot sync photos because your photos ligrary is not yet available. When I try to follow your instructions, I cannot select (Use as System Photo Library) button as it is greyed out. I only have one Photos library, but I do have an old iPhotos library. HELP!!

Sorry for the assumption, try holding down option when launching Photos to create a new empty library, then see if the option becomes available. If so selecting it might mean you can switch back to the primary library and then choose it as your System Photo Library.

tt2

I am having the same problem. {iMac - Mojave 10.14.6; iPhone 6, 12.4.2]. Created a new empty library and made it the System Photo Library. Attempted to sync from iMac to iPhone, but same error message. Switched back to original System Library.

Hmm. Try Repair security permissions for iTunes for Mac - Apple Community, but apply the fix to the Photos library you're going to want iTunes to open.

tt2

I've Designate a System Photo Library but it didn't help. I get the same error :(

Have you opened the Photos application since you updated to Catalina?

tt2

Still running Mojave, but iPhoneX is running 13.1.3

Not sure what else to suggest. Might be time to Contact Apple Support.

tt2