Mysterious folders that appeared in Documents on upgrade to Big Sur After upgrading to Big Sur today (from macOS 10.14 Mojave) on my 2018 MacBook Air 13&quot;, I found a number of unwelcome new folders had appeared in my Documents folder (when viewed with Finder).
These folders are:

GarageBand
Keynote
Numbers
Pages
Preview
QuickTime Player
TextEdit

Each one, except Preview and TextEdit, contains a single Alias file called &quot;iChats&quot;. The Preview and TextEdit folders are empty. Needless to say, I cannot open the iChats files.
I do not want these folders, but I can't move them to somewhere else, unlike my own genuine folders: a circle with a slash through it appears if I try.
So I thought I would look using Terminal, but cd Documents and then ls -a shows only my own files and directories. These unwanted interlopers are nowhere to be seen.
Edit: Some more information:
Following the advice of Joy Jin, I dragged each folder onto a Terminal window, to see what was revealed. The folders appear in Terminal as follows (every path begins with
/Users/davidhoadley/Library/Containers/ - I have edited that text out of each item below:

... com.apple.garageband10/Data/Documents
... com.apple.iWork.Keynote/Data/Documents
... com.apple.iWork.Numbers/Data/Documents
... com.apple.iWork.Pages/Data/Documents
... com.apple.Preview/Data/Documents
... com.apple.QuickTimePlayerX/Data/Documents

In answer to user3439894, yes, I can right-click and Move to Trash. But what then appears in the trash is the com.apple.(whatever)/Data/ folder, with several subfolders (i.e. not simply the folder from Documents that I described above). I do not know what these folders do, and I am afraid that if I delete them or send them to the trash, I will somehow adversely affect the running of the relevant applications.
So the folders appear to be some kind of link or alias. But they are not a unix-style hard link or a symbolic link, because they don't appear in the directory as seen from Terminal using the ls -a command.
So my question now becomes: is it safe to send them to the trash? And if anyone has any clues as to what the mechanism is that shows me these links/aliases/whatever they are, I would be most interested.
All of those folders could easily come from iCloud documents sync. You are correct to be cautious deleting them. I would be sure iCloud is signed out (or at least you don’t enable document sync) before trying to delete these.
We can’t really look at your iCloud settings, so a chat or call with Apple support would be prudent if you don’t see right away what happened to be sure you do not delete iCloud data.