How do I sort albums alphabetically in Photos.app?
If you’re talking about sorting your list of albums alphabetically, go to View → Show Sidebar or press ⌘ cmd ⌥ alt  S. Then right-click Albums in your sidebar and choose Sort → By Name.



If you’re asking about sorting the photos inside an album alphabetically, right-click that album in your sidebar and  choose Sort → Keep Sorted By Title. Note that most photos won’t have a title, and Photos will next sort by date taken.