The images above picture the result in Siril using the Auto-Stretch rendering mode. Note the improvement of the signal-to-noise ratio regarding the result given for one frame in the previous step (take a look to the sigma value). The increase in SNR is of [math]\displaystyle{ 21/5.1 = 4.11 \approx \sqrt{12} = 3.46 }[/math] and you should try to improve this result adjusting [math]\displaystyle{ \sigma_{low} }[/math] and [math]\displaystyle{ \sigma_{high} }[/math].