Running OS13.1 on MacBook Pro, M1

Just in case you should have enabled the shared iCloud Photos Library, you will only see the duplicates album, if you are viewing both your personal library and the shared library together. Otherwise the Duplicates Album is not available.

• If the shared library is viewed, the Duplicates album will vanish from the sidebar.

• and if the personal library is viewed, you will see a warning, when trying to view the duplicates album:

Photos in Ventura won't show "Duplicates" until if finds some. Could take quite a while. We're talking weeks, not hours.