M27

I tried it with other images, it's a bit tricky. And maybe my version isn't complete—many features just aren't there.

For stacking it's actually simple: you create a folder on your computer, inside it make 4 more folders named with English letters — darks, flats, lights, biases. Then you open Siril, click the house icon, select that folder, in the processes click "OSS preprocessing", and that's it, your work is done)

Thank you. I will definitely give it a try. The thing is, in this case I just have a sum. I did take darks, but they were 2-minute ones, so they didn't fit. Applying them introduced some artifacts in the image. And I didn't take flats either.