Duplicati is not really suitable for full system backups (which would include operating system files, application files, registry, etc). It works great for general user data files but I would not use it to back up OS, program files, or even MS SQL data.
At best Duplicati will make a general snapshot so that it can back up “open” files which may include SQL MDF and LDF files. But these would be crash-consistent backups, not application-consistent backups. Duplicati (as far as I know) has no intelligence when it comes to MS SQL and can’t ask the database engine to create an application-consistent snapshot.
It looks like you may be trying to do this so I just wanted to give a word of warning.
We may be able to provide some advice depending on exactly what you are trying to protect and what types of recoveries you may need. (Bare metal, complete system recover, … etc)