To work around the fact that there’s no unix/linux client: I make a “junction folder” on my Windows computer which points to the Unix server, and use Backblaze personal to backup everything. Alternatively, you could use Duplicati to make a local backup of the unix server to a windows PC, and then backup the windows PC (including the duplicati files) with Backblaze personal backup.
Of course, this depends on your setup, but my Windows PC is powered on frequently enough to make this work.