Your situation seems a bit of a special case, so see these other recent topics too:
Changing source OS (Windows to Linux)
Deleting Files on B2 not working because old DB not found (awaiting information)
Doing it on Windows would have been far more routine. Is old system still around?
Above posts get you around need of a backup, but not around your change of OS.
Note that a backup only uploads changes, so size growth may be small, but it also
means that delete of versions might not reduce size a lot. It does depend on use…
Are you low on space? If you can migrate the backup, it shouldn’t take much more.
Migration is kind of technical. Read first link on OS change for some of the options.
Going with full Windows and full Linux backup versions could use a lot more space.
Reusing at least current source file contents in the backup might use only what the
metadata (file attributes) need, because those are very different due to OS change.
EDIT:
Each one has a dlist file, and previous methods such as linked above seem to be
editing (maybe manually) each one, if the goal is to make them fit new Linux layout.
Although all of this internal surgery is poorly charted, I found another that might help
solve the too-many-dlist-to-edit pain. It uses DB Browser for SQLite on Windows DB
to search and replace in Prefix column in PathPrefix table to change to new way.
Duplicati Repair knows how to reupload dlist files that vanish, so I hid them and a
Repair replaced them with the versions with Linux paths. Very experimental though.
Before trying this, you’ll have to decide how much risk you want to take with backup.
If this is saying that GUI provides better lead-through, yes it does. CLI takes options.
Getting help from the Command Line Tools or the manual can help pick what to use.
If no
<filename>is specified, a list of all available backups is shown.
Restoring files from a backup is the equivalent GUI way to get numbers.
You might have built a database tied to the location, which could be used in the GUI as well.
You could look for your destination in text file ~user./config/Duplicati/dbconfig.json.
GUI database would initially have a database assigned, but no database yet, as seen by the
Delete button being unavailable (greyed out). You can save new path to CLI’s if you like that
and if you think sharing database is good. For independent GUI, Repair button will build DB.
You’ll then be able to do GUI Restore to specified folder, but more backups won’t be allowed.
The message will be as in earlier post in Changing source OS, and you decide how far to go.
Google search found some other examples of the message, if you’d like to see related topics.