Can't sync my iPhone Xs Max with iTunes 12.6.2.20 on Macbook Air (no updates available). Get message "You do not have permission to access iTunes" even after I've clicked "Trust computer" on my phone

Upgrade to iTunes 12.6.5.3 if you want to be able to transfer apps from your computer to your device. See Deploy apps in a business environment with iTunes - Apple Support for download links. What version of OS X are you running?

See also this post.

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For iOS 12 or later you need iTunes 12.8.0.150 or better running on OS X 10.11.4 or better. See How to upgrade to OS X El Capitan - Apple Support if required. iOS 13 likely requires iTunes 12.8.2.3 or better.

Assuming a suitable version of iTunes is in place then in Finder use the menu item Go > Go to Folder..., copy the following text, paste it into the dialog box and press enter:

/System/Library/PrivateFrameworks/MobileDevice.framework/Versions/Current/Resources

Unlock your device and connect it to USB. Double click on MobileDeviceUpdater in the folder that has opened. It should notify you of a software update. Install it and iTunes should hopefully recognize your device.

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