Advice about backup strategy

I'm relatively new to Unraid, and loving it. I've been slowly building up my Unraid box as a dual purpose NAS and Docker container host. However, I'm undecided about the best way to use Unraid as part of a backup system for my computers.

Here's the current situation:

• I have an HP Proliant server running Unraid. It holds my music and photo collections, and shares them via Samba to my computers.

• I have one Linux box (desktop) and two Macs (laptop and desktop) in the household.

• Currently, the computers back up to both attached hard drives and cloud backup (iDrive)

• I back up the Unraid settings/appdata to a different part of the array, and have now set up Duplicati (via Docker) to back that up to some Backblaze B2 storage

• I have some space on pCloud (lifetime purchase of 2TB when they had a steep sale)

What I would like to achieve:

• Back up each of the computers to a share on the Unraid array - a proper incremental backup with multiple snapshots

• Back up/copy/sync that backup periodically to an offsite location. That could be Backblaze B2 (which would get expensive quickly I think), or some storage like a Hetzner box which I could SFTP to or use S3 compatible methods. This would be less frequent and perhaps only storing a couple of versions, or even just the latest. I could continue to store the music and photos shares on pCloud because it is already paid for, they consume a lot of space, and those files change much less frequently.

• Continue backing up to hard drive, because it's easy and the fastest way to restore in case of issues.

• Stop using iDrive, because I would have a local hard drive, local Unraid server and remote copy of all my stuff.

• I'd like all of this to be scheduled otherwise it won't happen.

Ideally, I would like to use a backup solution that would work for all of those elements (so would be able to run on Linux, macOS and Unraid Docker container) for simplicity, but I'm also happy to use the best tool for each of the separate jobs if that makes more sense.

Does anybody have any suggestions for backup software for my use-case? I have leaned towards Duplicati because it works well cross-platform, but unfortunately it isn't yet compatible with backing up to pCloud (though that feature is in the development versions). I have also looked at rclone and restic.

Also, what's the best way to deal with backing up the backups? I am assuming that any backup solution is separating files into chunks to facilitate incremental snapshots, so would just doing a clone or sync work best to transfer a copy to offsite storage? Does this cause any issues if I ever needed to restore from the offsite copy?

Thanks in advance for any help and advice you can provide!