The Qt version was indeed not properly installed.
qmake expects a specific directory for target libraries
$ ~/Qt6/6.2.4/qnx/bin/qmake -v QMake version 3.1 Using Qt version 6.2.4 in /home/werner/qnx710/target/qnx7/home/werner/Qt6/6.2.4/qnx/libSo to fix QT Creator, I simply had to create a symbolic link:
$ cd ~/qnx710/target/qnx7 $ mkdir -p home/werner $ ln -s ~/Qt6 .