ON QNX, the tests (e.g., qqmlinspector) are being run from a host machine something like so:
ssh <user-id>@<ip-address> "cd <qt-tests-location>/qtdeclarative/tests/auto/qml/debugger/<debugger-test>; ./tst_<debugger-test>"

This runs the test in a non-interactive shell. https://codereview.qt-project.org/c/qt/qtbase/+/219602 took away the automatic addition of QT_LOGGING_TO_CONSOLE to the application environment. On QNX, this removal causes Qt to choose slog2 logging for the sub-process instead of stderr logging and the tests fail because the sub-process doesn't produce the expected output. Qt chooses slog2 logging because the sub-process is being run in a non-interactive shell.

You have to use QT_FORCE_STDERR_LOGGING=1 to make the sub-processes produce stderr output so that the tests work.