The update brings the ability to mark specific photos as favourite, with the changelog reading:
Favorites – Ability to mark your photos as you prefer using the special heart-shaped command. The tagged photos are collected in a dedicated folder called Favorites.
Besides an update to the app, the feature also needs server-side activation, so it may not be available to you directly.
Find the updated app in the store here.
[appbox windowsstore 9wzdncrfjbh4]