ms194 wrote:
.... and photos has be telling me to keep device plugged in while it looks for duplicate photos and curates. What's going on?
The "curating" is a new feature of Photos. Photos is using artificial intelligence to find the best shots in your Photos Library and compose pleasing layouts, without clutter, for the "Days" view. This is described here: macOS Catalina - Apple
Photos has a new immersive, dynamic look that showcases your photos and memories. See only the best shots in your library, without the duplicates and clutter. Browse your favorite photos by days, months, and years and get larger previews of all your photos. And Photos is even smarter, so it can highlight important moments like birthdays, anniversaries, and trips.
As Keith and OT wrote - it will take a very long time for Photos to analyse the scenes in each an every photo and video and pick your best shots, crop the photos for the tiled view, and omit duplicates and similar photos.
For my smaller test libraries with only thousand photos or so, it took several days. For my iCloud Photos library with roughly 50000 photos and videos it has never finished since I upgraded to Catalina last year.. It does not really matter. We can use Photos while this analysis is going on. It applies only to the Days view, that I am rarely looking at,anyway, because I do not like to see my photos cropped and without the titles below the thumbnails.