This is the digital equivalent of a safe; the "Unhide" button is the combination lock.
On iOS 16 and later, your hidden album is locked by default and requires Face ID, Touch ID, or your passcode to access. how to unhide hidden photos
Apple’s Photos app includes a dedicated "Hidden" album. This album is often hidden itself in newer iOS versions to increase privacy. This is the digital equivalent of a safe;
Here is how to perform the reverse spell. how to unhide hidden photos