Under my photos by year there is a cube which spins and it says: Curating Best Photos; Composing Layout; Gathering Favorites; Analyzing Scenes; and Detecting Duplicates.
I have been seeing this message "Composing Layout; Gathering Favorites; Analyzing Scenes; and Detecting Duplicates." stuck at 90% since September when I first installed Catalina. I do not expect it ever to finish for my large main library, if the library is large, as I tried to explain, and it not necessary to have it finishing.
I just tested again. I created a small photos library with only 3000 photos. And did not use this new Photos Library at all for two days, while I have been working with my main Photos Library.
After waiting for two days and not touching the new libary at all the new library has been showing finally this message:
But there is simply no way, that I could wait for weeks without touching my main Photos Library to get it to finish the "Curating". It has been stuck at 90% for my main Photos Library for five months now. here have been three system updates in between, that did not change anything.
And it is not necessary to wait for this to happen. It is a background process. Apple should stop this message from showing.
"Composing Layout; Gathering Favorites; Analyzing Scenes; and Detecting Duplicates. "
Ignore this message. This is just Apple showing off the new features of Photos in Catalina. These tasks are just required to create a pleasing layout for the Days, Months, Years. We can use these views, even while waiting for the curating to finish. I do not look at these views anyway, because the photos are cropped and tiled, the titles are not shown, and I cannot see them properly there, and only a subset of the photos is shown. The more useful "All Photos" view and the albums we create are independent of the curated views.
I have recreated my main Photos Library three times by downloading a fresh copy from iCloud, just to be sure, that the library has no corruption. But it did not make the "Curating" proceed beyond 90% either. It just caused more work, because I has d to recreate the manually added faces.