EDIT ignore this if you already have subfolders. I’m keying off the topic content, not the wording of the title.
Possibly what’s missing is a new folder button. Quick changes that would make new user experience a lot better.
While I can’t rule out a permission problem without knowing what user you run Duplicati as (root? you?), inability to make a new folder from this screen recently made me create it by hand using File Explorer, then I think I went Home and restarted the add because it was easier than figuring out exactly how far I had to back out to refresh.
This was all on Windows 10 with Duplicati running as a service which runs as SYSTEM – similar to root on Linux.
I think there’s a UI request to make this screen run more like cloud storage does, where there’s a base and also a folder within it. IIRC the peril was that without the extra guidance, people put two backups into the same folder.