What is Containers/com.apple.mail suppose to look like? My three-month-old MacBook Pro was upgraded to Big Sur as soon as it arrived, before migrating in accounts and apps from the old one.
It has since had several seemingly unrelated problems that do not seem to be hardware issues.  None of them happened on the old laptop with Catalina.
The worst is with Mail.app.  ~/Library/Containers/com.apple.mail has no extended attributes, and no ACL.  Finder will not let me see its contents (and no bypass on the contextual menu), but Terminal says I own it and the permissions are 776.  It contains only a Data folder and a plist.  The Data folder contains symlinks to several of the directories in ~.  And if I open Data in Finder, Finder changes &quot;com.apple.mail&quot; to &quot;Mail&quot; in the path.
I’ve been told it is not supposed to look like that.  But my oldest backup is more than six months old from the previous machine (which had Catalina), and it never had any of these problems.  I still have that machine, so tonight I charged it and looked, and verified that Time Machine is not lying to me.
That's why I'm asking. If your Big Sur is behaving well, do you have a similar ~/Library/Containers/com.apple.mail or is it very different?
The short answer is yes, I believe your ~/Library/Containers/com.apple.mail is what it is supposed to be.
Just like you, I do have ~/Library/Containers/com.apple.mail which Finder presents as one of 6 subfolders called Mail.  Mine has permissions like yours and same content including all the symlinks.
So don't worry, everything is (most likely) just as it is supposed to be.
The more worrying answer is that Apple Support staff mostly do not have the faintest idea about the changes in Big Sur.  I have come across other reports where Apple Support seems to be reading from their Catalina support notes.