Hi all, Founder/CEO DuckDuckGo here and I hope I can help clear this up. Search syntax filters are still available on DuckDuckGo and we’ve re-updated the help page to reflect that. Nothing has actually recently changed with the way they work in terms of removing any functionality. In fact, we actually recently added functionality to make site exclusion work better as described in https://duckduckgo.com/updates
What did happen is last month we temporarily updated our syntax help page because we had been getting complaints from some users that they were not working consistently and wanted to get to the bottom of it, but we never actually deactivated the features themselves.
Instead of removing that information from the help page, even temporarily, we should have said we know users are having problems and we’re working to address them. That's what the help page says now and we hope to provide an update soon.