I tried compiling with lcms2 and running a few tests, but unfortunately I’ve reached the usual point where I get confused and don’t understand anything anymore.
When I load the JPEGs or PNGs from “wide-gamut-tests,” the asset displays normally, but in the terminal I see these lines that I don’t know how to interpret.

file:/home/paz/wide-gamut-tests/P3-sRGB-color-ring.png
  err: Operation not permitted

file:/home/paz/wide-gamut-tests/R2020-P3-color-ring.png
  err: Operation not permitted

What does “unallowed operation” refer to?

What's even more confusing is that I get the same result whether I run cin with or without CIN_CM_PROFILE=...
If I use your command line:

CIN_CM_PROFILE="/usr/share/color/icc/colord/WideGamutRGB.icc"  /home/paz/cinelerra/cinelerra-5.1/bin/cin /home/paz/wide-gamuts-tests/*.jpg

Si avvia CinGG ma si apre una finestra di avvertimento con scritto:

int MWindow::load_filenames(ArrayList<char*>*, int, int, int):
Failed to open /home/paz/wide-gamuts-tests/*.jpg

In any case, I'm not quite sure what to do or what to look for. To verify that color management is enabled, should I see the horizontal stripes and the circle in the “color bars” and “color ring” images, or not?
Basically, CinGG behaves like GIMP 3 when “color-managed display” is enabled. In CinGG, there’s a slight difference between the same PNG or JPEG image, whereas in GIMP I don’t see any difference. Krita is like GIMP. Kdenlive is similar to CinGG, but I’m not quite sure how it relates to “color-managed.” It displays a message saying it doesn’t support image profiles.