New, useful feature for the Google Photos app is rolling out now،
You will receive this notification when Photo Stack is added to your phone
Since you only see the “top choice” of a stack, users may have a harder time seeing a particular version of a photograph they want to view. To do this, with photo stacks enabled, the user will need to tap on the stack and cycle through each photo in the stack. One way to make this a little easier is to search for a stack with a photo on it that is similar to the one you are looking for. Tap the stack to open it and go through each photo.
You can disable Photo Stack in the Google Photo app settings
If enabling Photo Stack becomes too much of a hassle, you can turn the feature off by opening the Google Photos app and tapping the profile icon in the upper right corner of the screen. Tap Google Photos Settings, then Preferences. If you have this feature, you will see a list that says “Stack Similar Photos.” It should be enabled by default and you can disable it by tapping the “Stack Similar Photos” toggle.