time machine - can't open .backupbundle with TM
I am trying to access an old file on my TM disk but TM itself doesn't recognize it anymore and if I try to open the bundle directly, I get a popup that says "The disk image couldn't be opened. The operation couldn't be completed. Operation not permitted." The icon of the file shows a closed lock in the lower left corner, leading me to think I could unlock it with sharing and permissions, but I can't make changes in the permissions pane.
I'm fine using Terminal but I have no idea what commands to execute to either unlock this file or to otherwise allow TM to read it.
This particular file was last altered in Nov 2021, at which time I retired it.
Any help would really be appreciated.
Tod
iMac 27″, macOS 12.3