You could study Duplicati vs. Syncthing (with versioning) by @JonMikelV, but when I followed its link to “File versioning (*Syncthing versioning makes copies of entire files)” it wasn’t quite what was asked for here. Then again, I’m not sure if I’ve ever seen a Windows program that’s the whole set. That totals to something unique.
The link-based approach seems more common in UNIX-derived systems than on Windows, possibly because links are better known, rsync is easier to get, etc. Windows tools are rarer, but I just found an interesting one proposed in Using NTFS hard links to combine full/differential backups as “ln.exe 's Delorean Copy”. I have never used it, but if you like links, this looks like a tool you could put in your toolbox, or script some for users.
To give an idea of how contrary to Duplicati’s current direction this is, let me point to its “Fact Sheet” where in my opinion the full described use case goes against the first 8 of 11 items. I think it’d be a big course change,
The design change in Duplicati 2 is described in Block-based storage engine but it held the Duplicati 1 goals.
There are other articles and developer documentation describing its technical details. Duplicati is still working on stabilizing its current design, and exiting from beta. It’s likely a poor time to go off into other directions now.
I believe some forum posts discuss use of Windows task scheduler to start a a backup when drive is plugged in, however (though I’m not a task scheduler expert) it seems like this could be combined with scheduled use.
I haven’t gone looking at what sync tools exists, but I did find a few Windows backups going in your direction.
RoboShot - my little backup tool (which is not looking very actively developing, but might still help somehow).
HardlinkBackup whose web site translation to English is here but I haven’t looked into its program languages.
You might be able to find what you want (if you do, please post), but I’m not sure Duplicati will head your way.
It’s not the call of the people you’re chatting with now. We might be surprised, but please review notes above.