Was Duplicati running as a service or tray Icon on the old system.
AFAIK By default the Tray Icon the System Database is either in c:\Users%Username%\AppData\Local\Duplicati or in the %AllUsers%\AppData\Local\Duplicati. Not sure as I always install as a service.
When Installed as a services its by default under C:\Windows\System32\config\systemprofile\AppData\Local\Duplicati
A point of note. If installing as a service in Windows10 change the default location to somewhere else as a feature Upgrade may clear that location. You can use the system Env Variable DUPLICATI_HOME or pass
–server-datafolder on installing the service.
I would suggest you install as a service, a reasonably good guide here
And copy your Duplicati-server.sqlite from Windows 7 into config location start the service and old config should come up. You should also export your jobs and retain a copy somewhere safe