[richorlin]

Just got the Kindle PW SE 12th gen yesterday and today I moved over 2800 side-loaded books from my 11th gen PW SE using Calibre. From Calibre I saved the "books on device" to a separate folder. Then I added them to a new Calibre library.
Then I uploaded them all to the new Kindle. The books show up ok and I can view them.
A couple of hours later this warning pops up. I have never had this with the older PW:
"Folder is almost full. One of the subfolders under Documents folder has exceeded 2000 items. To continue adding more items to your device, we recommend creating a new subfolder under Downloads."

Never had this happen before. Does this mean that you are limited to the number of books you can add to the Kindle? It shows only 13 gb used out of 25.
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Never mind....figured out the problem. I used the USB file manager (I'm using a Mac) and discovered that some uploaded books somehow ended up in the Download folder under a subfolder. Duplicates of what was already on the Kindle. Very weird.
Now, between the "send to Kindle" app and the "USB file manager" as the only way to actually see your Kindle, at least on the Mac, and the elimination of "USB Download & Transfer" I find it very inconvenient using the new PW 12th gen. Because of this, I'm seriously thinking about returning it.