I did some tests on an older android phone that I have. It's rooted so it makes easier for testing.

As you informed, iGO_World is not fully compatible. It can use the Arimi skin, but the ux folder isn't recognized after bootup. The "ux not found" that I got on my screen is really that. I even emptied the ux folder, renamed, to no avail.

Installing Avic is an alternative, since it's compatible and has ux, but... my car unit has the paths hardcoded. If I install Avic I can start it only within android apps menu. The mainscreen shortcut and faceplate buttons are hardcoded to iGO_World.

The logcat didn't helped to find why iGO_World doesn't use the ux folder nor showed any hint of an alternative named ux folder.