You enlightened me!!!
QRCodeDetector is from Objdetect class, I included the opencv2/objdetect.hpp, but I don't set the libopencv_objdetect341X library in *.pro file!

Qt Code: 
  1. LIBS += -llibopencv_core -llibopencv_highgui -llibopencv_imgproc -lopencv_objdetect -llibopencv_features2d -llibopencv_calib3d -llibopencv_imgcodecs -llibopencv_video -llibopencv_videoio -llibopencv_videostab
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Now it appears like a silly error, but I assure you I checked the libraries many times, spending a lot of time (more than one day), thinking the problem was totally different!

I'm using MinGW and yes, it uses similar logic to GCC (lib order affects the compiling process).
I tried Dependency Walker some time ago to check the deployment process, but I'm not very expert about it...

Thank you very much for your reply, and have a nice evening and weekend.