Mac users who use the Photos app to create photo books, calendars, and other photo-based products will need to find a new service provider soon, as Apple has quietly announced that it will no longer offer the products after September 30, 2018. Instead, Apple is now directing users to third-party extensions that offer the same functionality through other providers.
Those who have updated to macOS 10.13.6 and are working in Photos have seen a pop-up that says "To create a Photos Project, download a Project Extension". The extensions will provide a way to create new books, cards, calendars and prints from Photos content, and also have the ability to reprint existing projects.
In the past, those wishing to create a printed work just needed to select File > Create from the Photos menu bar, then select a type of project to being work on. The other project extensions have been available for some time:
Photos Print Products have been around since 2002 as part of iPhotos, but the explosion in the use of iPhones and iPads to view photos drastically reduced the demand for printed photos and products. Print Products were never available in the iOS versions of Photos, and are not included in the upcoming release of macOS Mojave.