Hello @barth, welcome to the forum!
According to How to install Duplicati on Synology / DSM it looks like the the DS216j does support Duplicati. 
Be sure to let us know if you run into any problems.
Hello @barth, welcome to the forum!
According to How to install Duplicati on Synology / DSM it looks like the the DS216j does support Duplicati.
Be sure to let us know if you run into any problems.