Photos app on Mac won't import photos from iPhone 12 (com.apple.IMageCaptureCore error -9956)

I recently bought an iPhone 12 and restored my old iPhone X backup onto it from iTunes. Now when I try to import my iPhone 12's photos into the Photos app on my 2015 MacBook Pro (macOS Mojave 10.14.6), I get the following error message for ALL photos:

This item cannot be added to your Photo library because it may be an unrecognizable file format or the file may not contain valid data.

The operation couldn’t be completed. (com.apple.IMageCaptureCore error -9956)

I've also tried this operation on my 2013 Mac Pro and got the same error message.

Please help! Thanks.

Brian