So it sounds like you could expect correct colors on a multi-monitor setup provided the program’s window is on that monitor, if you use @Carmelo_DrRaw’s photoflow package and the code works.
By “the macOS sRGB wall” I mean the problem that GTK+ applications in macOS are clamped to sRGB even if you use a wide-gamut monitor profile. That is what @Carmelo_DrRaw’s code above attempts to work around. More info in this thread: Wide-gamut preview in macOS