Quote:..big snip...Then a reduced shape is screened over in a different color, which will hopefully yield a uniform border around the second screening.
If it is just an outline then several ways for this. As Ofnuts described or the GEGL Drop Shadow filter with suitable settings.
However as your CAD experience:
For offsets to a path, (as ever) an old script, ra_offset_path.scm
Unzip the attached.
Put it in your scripts folder C:\Users\"yourname"\AppData\Roaming\GIMP\2.10\scripts.
Then it is a right click in the path dock, bottom of the long context menu. If you repeat it check that the dialogue has not popped-under the Gimp window.
Looks like this:
might come in useful sometime.