Undeletable file in Trash /Bin
A short while ago I was experiencing very slow downloads on my emails in macOS Mail. Following a tip in a forum I moved some system files to a new temporary location, these being automatically recreated by Mail when it was relaunched. The idea was to remove the cached settings. It didn't in fact help and I suspect that it was my email service provider (BT) that was actually the problem.
Once I was sure that Mail was working correctly I deleted the original system files that I had relocated. But when I came to empty the Trash one file remained, generating an error during the delete process. Thus began a long and unsuccessful attempt to get this file out of my Trash.
I found quite a bit of advice on the web, both from Apple itself and various technical web sites. I tried everything: key combinations, Safe Mode; Disk First Aid in Recovery Mode; Terminal commands and the clever idea of moving the file to iCloud and then deleting it on my iPhone after my iMac was powered down. But it just came back. I even moved it to the BT Cloud, which is outside the Apple system, and deleted it there, but it always returned.
Finally I found a web page that explained all. The file, in its orignal location, was:
I managed to delete the folders but DataVaults proved to be totally indestructible. The web page linked to another with an explanation of the additional controls that Apple has placed over access to files and folders in macOS Mojave, and of course in Catalina. My problems started when I was running Mojave and persisted after I recently updated to Catalina.
Here is an extract from the article:
DataVaults are folders to which neither the user nor third-party software has any access at all.
The only software which can see and work with their contents are certain Apple-signed products which have a specific entitlement to do so.