Nebulb performs stacking and noise reduction without using dark or bias frames, since they are not really necessary in landscape astrophotography.

The reason is that when an equatorial mount (star tracker) is not used, the sky moves slightly for each of the captured images and, therefore, when Nebulb aligns the stars so that they are all in the same position, the noise of the images moves. And precisely this "moving" noise makes it possible to remove it very well during stacking.

Another different thing is in deep space astrophotography using star-tracking mounts, since, in those cases the noise remains "static" and the use of dark and bias frames can be interesting.

That said, it is not strictly necessary to use them in many of these occasions.

This is an example of deep space photography without dark frames: