Yes, to creating a smart album, but if you don't know what photos are hidden, kind of difficult to put them in the smart album. Yes, using iCloud to synch across four Apple devices (Mac, iphone and two iPads). I can view the hidden album on both iPads and iphone but couldn't on the mac. All devices using same Apple ID, same network, all same settings. After revealing the hidden album photo on iphone first, followed by iPads, I was able to delete the items accidentally added to the hidden album using my iphone. Today when I booted the Macbook and checked Photos, the "Show Hidden Photo Album" is still grayed out EXCEPT when in full screen mode on Photos. When in full screen mode, I have the option to "Hide Hidden Photo Album" but there is no Hidden Photo Album showing (to hide) when this option is available. Seems like this is an iCloud synchronization issue due to the fact that all ios 15.5 devices function as expected, whereas the MacOS 12.4 version does not function correctly.