I tried delta.com but it wasn't able to find some international flights on their own alliance airlines. I called them about this and they confirmed this is done deliberately when booking using points. This made me lose confidence in delta.com and I went back to using Skyscanner.
(Yes it's basically a scam that their "partner" airline flights are hidden when buying with points.)
If your points are with Air France (another airline in the same "partnership") I believe you can. And if your points are with the exact same carrier as the flights you also can. But apparently points on one "partner" are not fungible with others, and you can't use Delta miles to book award flights on other carriers' websites.
This was when I found out that frequent flyer experts choose their "home" airline very carefully. To Delta's credit their points never expire...but if they block the flights I want what good are the points?
Their website offered me an alternative: fly with a different partner airline into the destination country then fly domestic on the airline that flies to the actual destination. That was bookable using (a lot of) points, but would make the journey twice as long.
(Yes it's basically a scam that their "partner" airline flights are hidden when buying with points.)