When searching for files, only the most recent backup is searched. Use this option to show all previous versions too.
--all-versions=<boolean>
Searches in all backup sets, instead of just searching the latest.
You’re doing a restore. Duplicati unfortunately doesn’t reject options that don’t apply to your action.
A Duplicati version is a point-in-time view of what was there at the time. Deleted files are not there.
What you wish for is a rare request, but it’s come up at least twice before. The key idea from these:
Do you know where in the file the data would be? If in the first block, you could just grep the raw blocks which would answer the question of whether the file is in the backup. Finding the file might be next step. This would definitely be a more technical method than just extracting all versions of all files with a script.
EDIT:
blocksize default is 100 KiB unless you changed it. You can also find your string in later blocks if you’re careful about the possibility that it might be broken across two blocks. So maybe you’d run two greps…