Share sheet won’t allow sending pdf or book or text file to iCloud, other locations

My iPad was recently upgraded to the new ipadOS and until this evening, things were working fine, including copying or saving items via the share sheet.

However tonight I had a PDF that I wanted to save in one of the folders listed, but rather than being saved, I got the message "The operation couldn't be completed. Operation not permitted." This message popped up no matter which local or iCloud location I chose the place the file. This also happened when I tried to save a simple text file, an image, and a .mobi book (I like to save Kindle books in my own library). I've never had a problem saving such files before.

I have not made any system changes or settings changes.

Is there something I can do to fix this?