Let me clarify about the Qt plugin vs command line question. The plugin takes the preview data from the host app (e.g., GIMP), which may or may not be a 100% representation of the image(s) themselves. The preview itself is rendered differently than the command line display. Both aren’t 1 to 1 to the actual output; CLI is much closer, so I tend to go with it.
My advice is to view the output in the final medium; e.g., if you intend on publishing to the web, then view it in a browser like Firefox with colour management enabled. G’MIC doesn’t do colour management, so not only are its previews not managed but CLI won’t respect the ICC profiles or transforms. This can be a headache to reconcile. My solution is to learn about colour and what G’MIC can do for you with that in mind.
Lastly, specifically regarding the patched based inpaint filter, I recall there being a mislabelling/misnaming of terms between the CLI (see help) and GUI versions, which can lead to some confusion. I brought this up a long time ago but @David_Tschumperle hasn’t made the adjustment.