How do I “unshare” icloud photos

Are the photos in a shared album? Or has a shared library been created, such as with Family Sharing?

it is also possible to share photos with a link, but that’s probably not related to what you are reporting:

• Share photos and videos with an iCloud Link on iCloud.com - Apple Support

Or are you possibly meeting the support for visual lookup?

• Find and name photos of people and pets on Mac - Apple Support
• Use Visual Look Up to learn more about a photo on Mac - Apple Support