Thanks for the instructions PC, i really love that result. I had a feeling Graphic Novel was in there somewhere.
The way it manipulates the circles is phenomenal. I think you have created a whole new style.

Also Layer FX may give good result (alas i lost the result in a Gimp -2,7 crash) the basic point is that the circles come flat but i prefer them with some depth (as with a bit darker at their center )

And to use Transparent BG for Circlism so could be overlayered in normal mode on top of a variant of the original
(i suggest a somehow simplified variant : Even the 2 Greycstoration preset , now in "testing and preset could be a good base .
then the colors of the BG must be similar but not identical to the dots color )

That make also the result more recognizable, trasforming "circlism" dots in a sort of brush effect, still strong but
with much less impact on the readability of the image

You must have patients of a saint to get the mixed circles and the colours together. I like the way you blend the colours in

patience is needed to wait circlism to render, i just go to do something else.
For the rest instead then use the eraser i added layer masks