What has worked for me the first time I’ve this problem: open your image. Select líneas mode. Under the preview, drag the first slider to the right. Surely you will obtain an almost black image. The open the histogram transform, from the menu or se icon. On this window you can tap on the button that has a curve with a gear superimposed. This will apply a real auto stretch transform in your image. Tap on apply button. Now in your preview you must see a not black image and if you save it as JPEG you can see that the new image preserve the same detail.
Obviously you will need other transforms, but I’m trying to give you the needed confidence in SiriL to keep learning. Yes, the curve is steeped at the beginning, but the results are very encouraging. This for example, is a 5 180” frames stacked and processed with SiriL.