I was disappointed to see that the Nokia 6 rear camera comes with a 16-megapixel resolution and 1.0 µm pixel size. An f/2 aperture is good, but Nokia was always known for its high-quality camera, so why Nokia has decided to use such a small sensor, or going with such a high resolution. Just look at the Nokia 1520, it has 20MP but it uses a large sensor and even with that very high-resolution, the pixels are larger (1.12 um). I don't know which sensor the main camera uses, but I know that Samsung produces the 16-megapixel S5K3P3 sensor that has 1.0 micron pixels and it's 1/3.06" in size. So I assume that the sensor size of the Nokia 6 rear-facing camera is also 1/3.06" (5.868mm), but again, I have no information about the exact sensor model used in the Nokia 6 nor a confirmation of its actual size.
The technology of the sensor matters obviously, but almost all mobile phone camera's sensor use BSI technology, and some are obviously better than others. The thing is that a sensor with such tiny pixels has no change to perform well unless the lighting conditions are ideal and there is plenty of light. Even Sony most advanced Stacked BSI CMOS sensors with 1.12-micron or 1.0-micron don't perform well in ow-light. The technology does improve over previous generation sensors, but if Nokia would have used a lower resolution sensor, I have no doubt that it would perform better and result in better low-light performance.
OIS and fast aperture can help because they allow the photographer to shoot in lower ISO using slower shutter speeds and get a well exposed image when shooting not in ideal lighting conditions, but there is a limit of how far you can go with it.
As of the time of writing, there aren't any official sample images from the Nokia 6 nor test photos uploaded by Nokia 6 owners to the Internet. I'm interested to know which sensor it is and how the camera performs in both low-light and daylight. I hope that Nokia would implement a sensor with larger pixels in its next phones and hoping to see a comeback of the PureView camera in its modern form, maybe a remake of the Nokia 808 1/1.2-type sensor but with 12MP resolution instead of 41.3-megapixel, this would be otterly amazing!