Macbook Pro M1 Pro, macOS Monterey 12.2.1
Zotero for mac 5.0.96.4
Zotero -> Preferences -> Advanced -> Files and Folders -> Linked Attachment Base Directory
I'm choosing the base directory. It seems like if I choose a directory "start with" the same directory of Data Directory Location, then it will be an error "You cannot select a Linked Attachment Base Directory within the Zotero data directory."

For example:

My Data Directory Location is /Users/hackroid/Workspace/Zotero, then I create another folder which directory is /Users/hackroid/Workspace/ZoteroFiles

Looks, they are two totally distinct folders under Workspace.

But I am not able to use /Users/hackroid/Workspace/ZoteroFiles as my Linked Attachment Base Directory.

But /Users/hackroid/Workspace/ZFiles works.

It seems that "/Users/hackroid/Workspace/ZoteroFiles" literally contains "/Users/hackroid/Workspace/Zotero" and the Zotero software just simply verifies one string whether contains another substring.