A logic issue was addressed with improved file handling. This issue is fixed in iOS 18.2 and iPadOS 18.2, iPadOS 17.7.3, macOS Sequoia 15.2, macOS Sonoma 14.7.2, macOS Ventura 13.7.2. Photos in the Hidden Photos Album may be viewed without authentication.
https://support.apple.com/en-us/121842
https://support.apple.com/en-us/121840
https://support.apple.com/en-us/121839