Changing smart albums thumbnail
Under the My Albums tab/drop-down list, on the side panel of Photos on my Mac. I have several smart albums I made of various years. One of these years, I would like to have a different thumbnail be the key photo of it rather than the one that was automatically assigned to it when I made the album (default first photo in album). After I find the photo I want to have the cover of that album be, I right-click it, but the option that says Make Key Photo is grayed out.
MacBook Pro TouchBar and Touch ID, macOS High Sierra (10.13.2), null