Ever since Google Photos and its unlimited high-quality cloud storage arrived, Google has included a handy backup method with your Google Drive. As long as you had the Google Drive toggle flipped in the Google Photos settings (and enough space in your Drive), everything added to Google Photos synced back to Google Drive, so you could create a personal library of photos in their original quality.
As of July 10, that's changing. Google says that Drive sync was causing confusion with users, so Photos will no longer include an option to sync with Google Drive. You'll still be able to back up your photos in original quality if you choose, but you'll no longer see new photos appear on your Drive. Similarly, anything you add to the Photos folders in Google Drive will no longer automatically appear in Google Photos.