Using the following test code:

#include <QCoreApplication>

int main(int argc, char *argv[])
{
qDebug ( "Debug logging Message ");
qInfo ( "Info logging Message ");
qWarning ( "Warning logging Message ");
qCritical ( "Critical logging Message ");
qFatal ( "Fatal logging Message ");

return 0;
}

Output with :
QT_LOGGING_TO_CONSOLE=0

1. QtQnxLogging
   Console:
   Debug logging Message
   Info logging Message
   Warning logging Message
   Critical logging Message
   Fatal logging Message
   Abort

slog2info -> no messages

QT_LOGGING_TO_CONSOLE=1

1. QtQnxLogging
   Console:
   warning: Environment variable QT_LOGGING_TO_CONSOLE is deprecated, use
   QT_ASSUME_STDERR_HAS_CONSOLE and/or QT_FORCE_STDERR_LOGGING instead.
   Debug logging Message
   Info logging Message
   Warning logging Message
   Critical logging Message
   Fatal logging Message
   Abort

slog2info -> no messages

QT_LOGGING_TO_CONSOLE=0
QT_ASSUME_STDERR_HAS_CONSOLE=0
QT_FORCE_STDERR_LOGGING=0

1. QtQnxLogging
   Console:
   Debug logging Message
   Info logging Message
   Warning logging Message
   Critical logging Message
   Fatal logging Message
   Abort

slog2info -> no messages

It may be related to this bug: https://bugreports.qt.io/browse/QTBUG-51378
It's probably also not working with Qt 6.0