@paulr In any case, you need a newer version of GIMP and G’MIC. An AppImage is available here: GIMP AppImage (continuous integration). I personally use @partha’s builds here: partha.com.
This is where this image came from when I do a reverse image search. The thread provides you hint on how to achieve the look, albeit in Adobe’s apps.
More samples of that look: http://benthomas.co/