I apologise in advance for any spelling mistakes as English is not my first language.
2. A little backtracking is necessary in order to understand the logic behind my image processing.
The difficulty with the processing of X3Fs is that they come to the SPP already modified. There are too many "degrees of freedom" in processing the RAW data, resulting in numerous postprocessing unstable results.
Sigma's numerous profiles (Standard, Vivid, Neutral, Portrait, Landscape, Cinema, Teal and Orange, Sunset Red, Forest Green, FOV Classic Blue), both in the camera itself and in the SPP, are clearly redundant for the work. You could compare this situation to artesian water from a spring. Instead of crystal-clear water you are offered water in lemon, apple or other flavours right at the well. But we want the best, pure and clean water, without any substances. What is why I think that profiles are always a bad thing. Also I should mention, that the names of the profiles are relative and are an indication of what the Sigma specialists have in mind for a particular workflow / scenes. But we look at the world with different eyes and what is good for Sigma may not be acceptable for us.
But in any way, you can't shoot without profiles. We have to select a profile in the camera that is closest to the shooting conditions.
This is my standard workflow in SPP and everyone is free to do as they like, disregarding what I write next.
Load X3F file into SPP.
1/ Set the following parameter - adjustment mode - X3F
2/ Then the most important - change the Color Mode to Portrait with values from 1.5 up to 2.0
I'll tell you later why I choose Portrait Mode for any situation.
Adjust the Tonal Adjustments parameters as you wish and check the items marked on the screenshot. Never use the Fill Light option.
3/ Save the file in a 16-bit TIFF. The color space is usually sRGB or AdobeRGB. It depends on the color reproduction capabilities of your monitor. PhotoRGB is ideal, but I've yet to see a monitor capable of reproducing all of PhotoRGB colours. In addition, for uploading to galleries and for photo prints, either an sRGB profile or special printer profiles are used.