

I don’t use it but I would recommend Kopia due to its content-defined chunking, deduplication, etc. I’m writing a fork of it that allows any Rclone adapter to work as the frontend or backend but it won’t be released for quite some time.
Otherwise I sync most my files to Backblaze by hand from time to time using Rclone and client-side encryption.

Define “server”:
If you mean any process that serves on the network well then of course you can.
If you mean multiple containerized stacks acting as a service then yes, you can do that too.
If you mean multiple operating systems, I’m not so sure but I can’t imagine that it’s impossible.