Can't sync my iPhone

Download the current 12.8 installer for iTunes from https://www.apple.com/itunes/download/.

Unlock your iOS device and connect it to USB.

Reinstall iTunes from the .dmg that you've downloaded.

During the installation it should announce that a further software update is required.

Install that and iTunes should see your devices.

See also If your iOS 12 device isn't recognized by iTunes, you might need to upgrade macOS or iTunes - Apple Support.

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