I think I see the issue.
In (1) The GEGL filter (exposure) is applied, Followed by the procedure - duplicate etc. Each duplicate has that filter attached. And that gives one result
In (2) the same GEGL exposure applied then merged with the image. The procedure applied and that is not the same effect as (1).
Is there a fix, apart from (2) I do not know.
EDIT: Just a thought. Apply the filter to the layer group as: (different computer, still Gimp 3 ) That is adjustable.
In (1) The GEGL filter (exposure) is applied, Followed by the procedure - duplicate etc. Each duplicate has that filter attached. And that gives one result
In (2) the same GEGL exposure applied then merged with the image. The procedure applied and that is not the same effect as (1).
Is there a fix, apart from (2) I do not know.
EDIT: Just a thought. Apply the filter to the layer group as: (different computer, still Gimp 3 ) That is adjustable.