ChatGPT 4 said it was under “Arrays & Tiles”, called “Resize” … it was not. Then it said it was under “Geometry” but I couldn’t find that either. So much for AI … 
Pardon my ignorance, I would have thought that re-sizing would be an easily-found basic function.
IMHO you are better off using the Gimp scale algorithms NoHalo or LoHalo separate from the gimp_gmic_qt plugin.
However, if you use the gmic dialogue search for scale, there are options. Some specific for scaling up and a more general scaling down option.
This last one by Photcomix, who sadly vanished while on holiday about 10 or 12 years ago, it does work but is a bit “old-fashioned” these days. No/LoHalo for example does the pre-blur for you.
…you can also use custom code.
Not often I delve into the gmic documentation but this seems to work (for downscaling)
shrink_xy
Never trust what ChatGPT says, that’s bullshit most of the time (and 100% of the time when it comes to G’MIC stuffs 
).
We didn’t add a generic “Image Resize” filter in the G’MIC-Qt plug-in, as, as you said, this is a very basic functionality so it’s already implemented in all host software.
Thank you both for your helpful responses.
My purpose was to resample an image upward with various apps and methods and compare results.
Thanks especially for pointing out the G’MIC ‘Search’ function which I had never noticed, duh!
Searching for “upscale” did the trick !
