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Welcome to Android Central! Just to be sure, open your Camera pp, then tap More at the lower right (next to the Video option). Do you see Night Sight there?
Welcome to Android Central! It won't work miracles if there's almost no light -- there still has to be some degree of ambient light. Show us a couple of images side-by-side, one with Night Sight, the other without. Here's an example on my 2 XL: