Thank you. I finally got it working by installing it to (as you showed):
GIMPPortable\App\gimp\lib\gimp\2.0\plug-ins
In GIMP's preferences, it listed the plugins folders as
GIMPPortable\Data\.gimp\
and
GIMPPortable\App\gimp\lib\gimp\2.0\
I know I had tried the first location (under the plug-ins folder there), and thought I'd tried the second too, but am not sure at this point. Also, when I posted that, the current version of gmic was 3.4.3, whereas it's now 3.5.0, so that change could be a reason too.
FYI, I'd also previously tried:
C:\Users\me\AppData\Roaming\GIMP\2.10\plug-ins
GIMPPortable\App\gimp\lib\gimp\2.0\plug-ins
In GIMP's preferences, it listed the plugins folders as
GIMPPortable\Data\.gimp\
and
GIMPPortable\App\gimp\lib\gimp\2.0\
I know I had tried the first location (under the plug-ins folder there), and thought I'd tried the second too, but am not sure at this point. Also, when I posted that, the current version of gmic was 3.4.3, whereas it's now 3.5.0, so that change could be a reason too.
FYI, I'd also previously tried:
C:\Users\me\AppData\Roaming\GIMP\2.10\plug-ins