Could not execute plug-in “gmic_gimp_gtk”
(/usr/local/lib/gimp/2.0/plug-ins/gmic_gimp_gtk)
because it uses an obsolete version of the plug-in protocol.
Have you tried any of the binaries here? I often use them to replace what is packaged with GIMP. You could even have multiple plug-in versions of G’MIC if the file is named differently as long as it is in the right directory.
I read the article. I might be wrong, but based on personal experience, I believe that G’MIC GUI makes the assumption that the input file is sRGB and in the range of 0-255 because the default GIMP does that. However, I haven’t had problems with linearity or posterization because internally, G’MIC doesn’t make any assumptions and works in 32-bit floating point precision.
The article is out of date. gmic changes in lock-step with default gimp. cce is behind default gimp. I am not able to do enough typing to fix these issues. Use the appimage or use default gimp.