So my original problem is that I have one project where multiple files from different folders have the same name. I cannot change the names because those folders are part of a library that was previously compiled with visual studio that I am trying to transfer to Qt creator (with a qmake based compilation).
I saw that when CONFIG += object_parallel_to_source is used the .obj are suposed to be placed in a replica of my project structure which solve the problem of the files with identical names.
During the compilation i had linking error message telling me that some .obj files couldn't be found.

So I tried it with a simpler project:
project_folder:
->main.cpp
->subfolder:
->->func.h
->->func.cpp

with the func.h & .cpp defining a simple "hello world" function that is called in the main

The .pro file contains the following lines:

CONFIG += console
CONFIG -= app_bundle
CONFIG -= qt
SOURCES += main.cpp \
        subfolder\func.cpp
HEADERS += subfolder\func.h
CONFIG += object_parallel_to_source

When executing Qmake it indeed create all the new folder for the compilation.
But when compiling I get a linking error indicating that the file func.obj can't be found:
LNK1104: cannot open file 'debug\subfolder\func.obj'

And indeed the files doesn't exist. And when checking the copilation steps the func.cpp file is not compiled ...

Is there anything I did wrong to use the object_parallel_to_source option?

Ah and I precise, I'm not compiling with a shadow build (but I tryed it also and it doesn't works anyway)