how to launch recent Jupyter QtConsole on Windows without a console window

There are two problems here:

• %CONDA_PREFIX%\Scripts\jupyter-qtconsole.exe marked as console executable (Subsystem field in PE optional header)
• the -m ipykernel_launcher <etc> subprocess started with python.exe even if the launcher was started with pythonw.
  • This one I was able to track to %CONDA_PREFIX%\share\jupyter\kernels\python3\kernel.json. It uses a full path to the executable thus doesn't trigger the logic in jupyter_client\manager.py that replaces certain patterns with sys.executable.

Both of these are specific to Anaconda and do not happen with the stock Python. As such, file a bug against https://github.com/conda-forge/qtconsole-feedstock to get this fixed.

These are the workarounds:

• For the first bug, run pythonw <Scripts_dir>\jupyter-qtconsole-script.py which is the script that the .exe wraps.
  (This is Anaconda-specific. Regular Python uses a different wrapping mechanism. Anaconda must be patching setuptools or something.)
• For the second one, replace the full path in the aforementioned kernel.json with "python". This change will be overwritten when you update the ipykernel package that this file belongs to (this can be checked by searching for it in %CONDA_PREFIX%\pkgs).

The OP reports that this solution may break other Anaconda packages. I believe those that break make assumptions about the availability of standard streams. Though it too counts as a bug in my book, it must be coming from the fact that Anaconda packages aren't tested with this setup.

To create a shortcut/batch file to run the above command in Anaconda Prompt environment, see e.g. How to make batch files run in anaconda prompt.