Ok I didn’t understand very well. Imagine you want to make a picture of a waterfall. If you take 100 shots of 1/100 sec, you will have in each of them some different water patterns in the main stream of the waterfall and some droplets that are in different positions all around it. If you use an outlier rejection, you will likely remove all the droplets that are outside the main stream, that you normally see in the minutes long exposure. Using the average stacking without rejection should work fine, and there should not be a lot of outliers in daylight images anyway. If you still want to remove dead pixels, the cosmetic correction filter of siril will just do that.
That may indeed work quite well 