google storage only, can it add rclone as backend to support other storage providers?

Huh? No... Kopia supports cloud object storage, google drive, webdav, SFTP (ssh), or it's own repository server. https://kopia.io/docs/repositories/

I just use SFTP.

Thanks! seems great to me. It's going to switch kapio-ui from electron to go-binary-plus-browser, I thought its server already provides a browser UI, not sure why it needs a new desktop UI that is browser based, why both.

Yeah, I was wondering about how Duplicati compares to Kopia, which seems to check pretty much all the boxes for me.

Can recommend kopia as well. It is the one that I settled with after trying out pretty much all the other open source solutions (at the time).

Works great across all my devices (win, mac, linux).

Unfortunately looks like it does not backup full metadata (ACLs, extended attributes, flags, alternate data streams, special files, etc).

I wonder if there is any program that does?