I sync all my device files to a local Freenas server which runs duplicacy in a jail and sync's it every night to backblaze B2. I looked at duplicity, restic, attic, borg and in the end settled for duplicacy. Pay attention to the duplicacy license, for somebody it could be a problem.

I do this, though not from Windows, just Mac and Linux. I use restic, which has B2 support smd handles all the encryption. it also does diffing for backups. There's a Windows build, so I assume it would work for you there as well.

You can view and download builds at https://github.com/restic/restic/releases/

I don't automate this though, I just use it for occasional backups. Not sure what the automation story around restic is.

Similar to the other two sibling comments, been using restic to sync to B2 over the past 6-7 months. Stored amount has been 450-475 GB, and total costs tend to be about $2.50-$2.75 per month.

Yes. I use restic same as the sibling comment.

Have >8TB of data from multiple machines with a lot of deduplication (source is somewhere around 10 to 12TB).

I use Arq on two macs and it works very well with B2.

I use and like Arq also, but the OP asked for something that covers Linux, which I believe Arq does not.