Siril gives you the option to write a tiff file with or without appending an ICC profile. However, Siril is not color managed so appending an ICC profile to the image data does not make much sense IMHO. I think you might find this discussion helpful Siril Colour Management
Right, a color managed application like darktable will apply the sRGB TRC to the data accordingly even though the data is not sRGB. In addition, Siril does not apply the display transform to the image data rendered in the preview. Therefore, the Siril preview image is not actually linear.
The raw image data loaded into Siril will be in (linear) camera RGB. Siril does not apply a color correction matrix (CCM) like other raw converters such as darktable. Therefore, if you are only applying calibration frames (darks, flats etc) and staking lights then the final staked image will remain linear camera RGB. However, applying operations like photometric color calibration or a histogram stretch will shift the data into a different (local) color space - but most likely not sRGB.