I posted already a question in darktable forum, how to achieve pure b&w (no grayscale) image in dt.
I decided to post my image also here, to get other views on how the image could look. The target is to have an image with only black or white pixels (no grays). You can see my work below. A practical tip I have noticed is that you need to crank up the local contrast far more you would do with normal processing.
Images licensed CC BY-SA 4.0.
P8141543.ORF (17.4 MB)
P8141543_02.ORF.xmp (10.8 KB)