Opens an image in gmic, default color presets are the PIXLS pack as has been usual. Filters in that pack seem to all work. But try to switch to another pack and, while it shows the author’s name, the choices of the individual filters are the same as in PIXLS. And none of them work either.
Similar behavior in the film simulations: Black and white opens by default, and those filters work. But you can’t open any filters from any of the color packs.
This has been also reported here : GitHub · Where software is built
I cannot reproduce this bug on my Ubuntu install, and apparently it has been solved by the OP. Not sure what is happening here.
I see from the other report itat have occurred on the Arch Linux version. That squares with my situation in that I’m running Manjaro. I still don’t know how to fix the issue tho
Same problem here on arch with gmic/gimp-plugin-gmic 3.5.4-1.
The only workaround I’ve found is to use the “Apply External CLUT” in gmic gimp.
You can download your favorite color presets here : https://gmic.eu/color_presets/ and put them in ~/.cache/gmic.
(you can put theme in a different location, I’m just using the same folder that pre-gimp 3 stored those filters)
There seems to be a tiny difference between haldCLUT and cube format when using the same filter but it does the job.
I had a little time this morning to test this problem on Manjaro, and found that the version of G’MIC-Qt available in the official package (Arch Linux - gimp-plugin-gmic 3.5.4-1 (x86_64)) did indeed have this bug.
What’s surprising, though, is that when I tried to compile the plug-in myself directly from the sources (still on Manjaro), I ended up with a working plug-in that no longer had this bug!
The beginning of an explanation: to compile the plug-in I used Qt’s qmake, and not cmake (which is used to build the Archlinux package).
I don’t really know what’s going on, but as I don’t know anything about cmake (and I’m not interested), I’ve moved the files corresponding to the cmake configuration into a ‘cmake_broken/’ directory. I hope this will encourage packagers to use qmake instead, which just works fine.
Sébastien, the developer of the G’MIC plug-in, passed away last October, and I’m afraid his code can’t be maintained for very long (I don’t know anything about Qt, cmake and all the other technologies he used, and I don’t have the time to delve into it).
So far, so good… But for how long?
OK, so it seems that this issue happens only when compiling with Qt6 (instead of Qt5).
This has nothing to do with the CMakeLists.txt.
I’m investigating, but I’m definitely a noob when it comes to Qt, so any help would be appreciated!
Qt6 is a major platform upgrade and I wouldn’t expect to just change and have everything work.
Found and fixed!
Pheww, I’m quite happy with this one, it was not simple to spot.
And it looks like everything works now as expected, even with Qt6. So far, so good! 
Minor release 3.5.5 expected tomorrow!
Antonio, the packager of G’MIC-Qt for Arch has been super-reactive, and you now have G’MIC 3.5.5 available in the official Arch repo, where this bug has been fixed!
Thank you David for the additional details !
Got gmic updated and so far so good : colors presets and simulate film work like a charm.