This new feature may help some situations, though it’s not really the OP request:
This version adds support for configuring multiple destinations for a single backup job. This allows you to backup to multiple locations simultaneously, such as a local drive and a cloud storage provider.
A downside of it is that the cloned backups inherit any issues in main destination.
Duplicati Documentation doesn’t seem to cover it yet. Meanwhile the blog post is:
Blog post: Built-in 3-2-1 backups through Remote Synchronization
Trigger Modes: When Synchronization Happens
looks like it can do sophisticated scheduling of the sync, though not of the backup.
I haven’t seen GUI support to help with this setup. It’s possible that I just missed it.
For any who really want something like a backup source set instead, you could try:
Scripts (and share one script between your jobs):
--localpath = "new value". is the source set.
--include and --exclude will customize filters.