To address the original question: Yes, the red light districts are open but quite why you would want to come here at the moment is another matter. Unfortunately the kind of tourists who choose to visit right now are those who don't care a toss about the current COVID situation. Mostly young Germans with some Belgians, UK and Irish. Social distancing in Amsterdam Centrum is absolutely non-existent (and has been since beginning of July when restrictions were lifted). Of course, cases have spiked in recent weeks including several at a student society in Warmoesstraat, announced yesterday.
From tomorrow, mask wearing is mandatory in many busier areas of the city including the main red light area, De Wallen.
Consider coming another time.