I tried FreeNAS, unfortunately it was during the Corral debacle so I ended up going with unRAID instead. I’m happy with it so far (though would have preferred free.)
It also supports Docker so I have set up Minio (yep, it was easy) but haven’t actually connected Duplicati to it yet. Luckily I have a fixed IP & domain so don’t have to worry about dynamic DNS.
The interface limit feature has been discussed and requested, but I haven’t seen much work done with it.