The Shared iCloud Photos Library is only visible in your own iCloud Photos Library, using the same Apple ID you have used, when you set up the shared iCloud Photos Library. Are you currently viewing your iCloud Photos Library? And is "Shared Library" enabled in the Photos > Settings in the "Shared Library" tab of the Settings? If the Shared Library is no longer turned on for your iCloud Photos Library, try to turn it on again:How to use iCloud Shared Photo Library - Apple Support
The Shared iCloud Photos Library has some limitations. You can only have one Shared Library at a time. Before you create a new Shared Library, or can join a different Shared iCloud Library, you have to delete your current shared library. And you can see the photo from the Shared iCloud Photos Library only on devices with a system version, that supports it. On a Mac with macOS 10.13 Ventura or later, or an iPhone or iPad with iOS 16/iPadOS 16.
When you join a Shared Library, Apple is automatically creating a backup, but this backup is only kept for six months. It will be gone by now.