I have a photo library with 700,000 photos in it - and many of them are duplicates.

I am certain I'm missing something obvious, but there are a couple of things I'm having trouble figuring out.

#1. In album view, I have a folder for each year, and then within that folder, an album for each day on which I have photos.
From the view menu, I enabled "Include album sub-tree" so I see all of the photos for the entire year, when I select the year - but this selection doesn't seem to work for the "Find Duplicates". If I try to "Find Duplicates" with only the year folder selected, it doesn't find any. I have to drill down and select all 365 albums for that year. Is there a way to avoid having to do this?

#2. Once I've run the "Find Duplicates" on an album or albums, the "duplicates" tab appears and I see one row for each photo with duplicates, and then in the main area, I see all 8 photos (of which one of them is labeled "reference image"). The action I want to take for each row is to automatically delete all of the duplicates EXCEPT FOR THE REFERENCE IMAGE. But I can find no way to automate this process. So far the best I've been able to do is to click on each row (one at a time), then do a select all, then de-select the reference image, and then right-click to tag the others as "duplicate". But surely there has to be a way to automate that process? I will have thousands of images which are duplicated and there has to be a way to deal with them better than the way I'm doing it now, right? Please share it with me - or point me to the documentation that explains how!

Thanks in advance.

I assume you are referring to "digiKam"? Take a look at "FDupes" or the newer "jdupes" for comparison.

I think the weapon of choice here is:

https://github.com/qarmin/czkawka

Searches for exact dupes (by hash), or, which I like very much, it can also search for similar images/videos. The latter saved me already gazillions of space by finding different copies of of the same movies

No install needed, it provides also appimages.