"Camera Format Changed to High Efficiency your Mac is no longer syncing with iCloud photos, camera will capture in high efficiency Format”.

Hi there leighmiller,

Thanks for joining us in Apple Support Communities. We understand you're seeing an alert about the format for Photos on your Mac. We're glad you've connected with us, and we can provide some guidance.

"If you're using iCloud Photos with iOS 10 or macOS Sierra, you might see a warning icon in the upper-right corner of the photo or video, or you might see an alert message. To fully view, edit, or duplicate HEIF and HEVC media on your device, upgrade to iOS 11 or later or macOS High Sierra or later." Have a look at this link to learn more:

Using HEIF or HEVC media on Apple devices

Keeping that in mind, you'll want to be sure your iOS devices and your Mac are all updated to the latest software version. The links below provide more information:

Update your iPhone, iPad, or iPod touch

How to update the software on your Mac

We hope this information is helpful. Don’t hesitate to let us know if you have any more questions.

Take care.