Can't really help very much with manjaro linux, not one I am familiar with, although I have just installed it in a VM.
You installed what? A gimp-python package ? Does it also install python2 ? Check that, doesnt in other linuxes.
layerfx.py is in ~/.config/GIMP/2.10/plug-ins/ ? It is marked as executable ?
Attached an updated for Gimp 2.10 version, take the old version out, unzip, should already be executable but check anyway.
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Just a try out in manjaro but using a 2.10.22 appimage from https://github.com/aferrero2707/gimp-appimage/releases/
Wanted to see if (1) It worked - it does (2) my gimp_gmic_qt plugin compile worked there - it does.
looks like this: https://i.imgur.com/uyGls0r.jpg Think I will stick with kubuntu for the moment
You installed what? A gimp-python package ? Does it also install python2 ? Check that, doesnt in other linuxes.
layerfx.py is in ~/.config/GIMP/2.10/plug-ins/ ? It is marked as executable ?
Attached an updated for Gimp 2.10 version, take the old version out, unzip, should already be executable but check anyway.
---
Just a try out in manjaro but using a 2.10.22 appimage from https://github.com/aferrero2707/gimp-appimage/releases/
Wanted to see if (1) It worked - it does (2) my gimp_gmic_qt plugin compile worked there - it does.
looks like this: https://i.imgur.com/uyGls0r.jpg Think I will stick with kubuntu for the moment