QNX Platform Notes should be updated to QNX 7.0, but it still mentions QNX 6.6.
Also "If Qt does not use fontconfig, you have to specify the path to the fonts provided in Qt and set QT_QPA_FONTDIR to <Qt-install-path>/lib/fonts" should be more like: "If Qt does not use fontconfig, you have to specify the path to the directory containing fonts and set QT_QPA_FONTDIR to it or place fonts to <Qt-install-path>/lib/fonts which is the default location." meaning, that by default Qt looks in <Qt-install-path>/lib/fonts if the QT_QPA_FONTDIR is not set.