Maria Folsom wrote:
the trash is 'empty,' except that it's not. A folder still remains. This untrashable folder contains something nested in other folders call 'boot.efi.'
Computer runs fine, but I'd like to learn what's happening, and what that stubborn file in Trash is about. Thanks to anyone who has time and patience to help me figure this out.
boot.efi is the boot loader, that is part of the system files used during startup when the Mac is powered on. In your case, should be the copy saved by Time Machine on the backup disk.
Since you screwed up your TM disk, performing the operation you described, I would recommend to reformat the external disk and start over a fresh new backup.
The boot.efi should go away as soon as the external disk is ready again.