Yet another CP Orphan. I will be moving to CP for Small Business but I need to find a solution for friends that were backing up to me. All are on Macs. I was thinking about setting up a Minio server on my macOS Server and let them back up to that with Duplicati. Anybody in the same boat?
I don’t know about your boat exactly, but there are others doing something similar to what you describe. For example, here’s a How-To for setting up Minio on Linux and Duplicati on Windows:
Duplicati CAN back up extended attributes, however I’m not sure if the Access Control List attribute is included in that. Somebody more familiar with the Linux / MacOS side of things might know, however…
Yes, that’s how I came across Duplicati. I think it looks all very good for a rather new product.
Having been playing with it for 1-2 days,my biggest hurdles are: a more professional retention scheme (but it’s in the works), a lack of description of all the options (and a description in general, e.g. for my extended attributes question — this is important on the Mac because there are still files for certain apps that have much of their information in extended attributes so can only be properly backed up with them), and a lack of macOS implementation information in general (e.g. setting up a system-wide backup).
I’m glad you found us!
Yes, we’re working on a few things from your list but not as quickly as we would prefer. 
I’m not sure you found it or but but three is a manual in the works. You can see some versions of it linked to at:
I’ve been looking at version 0.5 of the manual.
So, how do I find out what Duplicati does with extended attributes, etc.? It can do it, but will it and what is needed to make it do that? And which attributes does it store? E.g. will it store extended attributes on a macOS HFS+ file system? To have a reliable backup on macOS requires storing extended attributes because some applications require these for correct functioning.