Gmic not opening with latest GIMP (using either Stable or the latest Dev Version)

Which OS are you running? Windows 10? And which GIMP is it and how did you install it?

I use the portable version of the official GIMP in a custom directory. You can drop the G’MIC zip contents in GIMP 2\lib\gimp\2.0\plug-ins\gmic_gimp_qt.