It could be theoretically possible to run multiple parallel backups to separate directories with Duplicati in command line mode, with care, no deduplication possible. But would it fit your needs ? How could I know ? Organizations are paying experts good money to find the best solution for their needs, they have extended access to how the organization work, and sometimes the ‘experts’ are getting it badly wrong.
You will note that I am neither paid good money to discuss your needs, nor I have any access whatsoever to the facts on the grounds for your problems, and the first aspect explains why I have no interest to get more involved in the second.
The df command (unlike du) measures the filesystem (is T for terabytes?!). How big is actual source? Duplicati’s defaults are currently performant to 100 gigabytes, but blocksize can be scaled up some.
I’m not following that idea. The B2 CLI is not a backup tool, although it seems to have sync capability. Backblaze B2 Integrations and other resources give an enormous list of software if you’ve chosen B2.
There’s one I see missing, but I don’t know your scale, your business dependence (if any), and so on.