What will be an easy way converting digitized negative images to positive images?

[rich2005]

gimp_gmic_qt download the latest 3.4.3

https://gmic.eu/files/linux/gmic_3.4.3_g..._amd64.zip

Unzip and put the gimp_gmic_qt folder in your plugins folder.
That is in your home folder ~/.config/GIMP/2.10/plug-ins

Scripts
Unzip the attachment Then scripts go in the scripts folder ~/.config/GIMP/2.10/scripts/

It seems that nothing works for you, so I will not be surprised if these are the same.