I've seen some sample images taken with the Nubia Z11 Mini S primary camera on gadgets.ndtv.com website. The low-light performance was more or less what I expected it to be, mediocre. It's not bad, but not great either. The f/2.0 aperture does of course help here. This means that you can still be confident that the camera will be able to capture details and well-exposed shots when the sun starts to fade out into the horizon.
I was much less impressed with the nigh shots, and this clearly shows the limitation of the Sony IMX318 (1/2.6", 22.5MP) sensor. This sensor has very small 1.0 micron pixels. This sensor was designed to deliver excellent images in daylight, but it's not optimized for low-light photography. Night shots were very blurry and all that humongous resolution isn't worth it when the pixels can acquire enough light to produce a well exposed image with sharp details. This is a problem not just with that particular sensor but with many phones that come with a high megapixel resolution camera and relatively slow aperture lens. F2.0 aperture is very fast, but in order to obtain good enough exposure, the ZTE Nubia Z11 Mini S camera should have had a f/1.7 aperture.
It's funny when you see images taken in daylight versus one taken in less ideal lighting conditions. In daylight the Z11 MiniS produces stunning, vibrant and very detailed images, when the sun sets, it's exactly the opposite. This is something that you had to be aware of before buying the Nubia Z11 mini S. If you love photography and find yourself shooting quite a lot of your photos in the evening, I don't think that this phone camera will be a good choice for you. It's better to look for phone with a primary camera with a lower resolution sensor and with f/2.0 lens. The sensor technology also matters, but nothing is worth more than watching camera samples and see how it performs with your own eyes. This is exactly what I do. I read the specs to educate myself and know what I am actually buying, but I look into the sample images to see what can I expect from the camera when I start shooting it myself, if I had the device. This is what reviews are for and the sample images are really important. Maybe you'll find the low-light performance adequate for your specific needs, I just didn't. This is a camera for daylight photography that can squeeze out decent images in late afternoon, but at night it's just not good enough in my opinion.
You can check out the sample images shot by gadgets.ndtv.vom and see it for yourself.