Select and unselect photos in Photos on Mac
You can select and unselect photos in a variety of ways.
Select a single photo: Click the photo or press the arrow keys to quickly navigate to and select the photo.
Select a group of adjacent photos in a moment: Click the first photo, then hold down the Shift key while you click the last photo. You can also hold down Shift and press the arrow keys, or simply drag to enclose the photos within the selection rectangle.
Select photos in a moment that are not adjacent to each other: Hold down the Command key as you click each photo.
Select all the photos in a moment: Press Command-A or choose Edit > Select All.
Unselect specific photos: Hold down the Command key and click the photos you want to unselect.
Unselect all photos: Click an empty space in the window (not a photo).