Hello @europlatus,
Just in case you are interested (otherwise feel free to ignore it)…
There is a G’MIC filter which can also accomplish this task: Red-Eye Attenuation.
You only need to select the eye, with GIMP, and run the filter afterwards.
Here is a screenie (GIMP 2.10.18 - G’MIC 2.9 on Windows 10):
