Photos

You indicate in your post that you are using macOS 12.7 Sierra, is that correct?

Since Ventura (OS 13) Photos has automatically scanned for duplicates and, as muguy said, those appear in a special Duplicate Album. But before Ventura, we were on our own.

An example of 3rd party software, like muguy suggested, is PowerPhotos ($30) which does lots of useful stuff, and which many of us still use for things other than just duplicate finding.

Be careful! There are lots of duplicate finders and "cleaners" that can really mess up a Photos Library. PowerPhotos works with the Photos database properly, and it is fully dependable.

Open Photos

look for the duplicates album

duplicate checking is part of the latest MacOS releases. Make sure that your system is up to date. Otherwise, you’ll need some kind of duplicate finding software.