I recently came across an open-source tool called Czkawka that does a bunch of useful processing on a given folder(s) of photos, including deduplication.
In my recent migration to manual organization I wanted to make sure that I didn’t lose any photos so I imported my Photostructure library to Digikam before switching over to using my Digikam library as a manual source for my Photostructure library. Needless to say, this meant I had a huge number of duplicates.
Czkawka is written in Rust and in my experience is very fast, utilizing every core on my machine (first time I “niced” a process on this machine). It did a great job of finding duplicates and I even used it to find a few “similar” photos and delete them.
Anyway, wanted to recommend this for others as it was greatly useful for me.