I've added PR 9516 that just clears __PYVENV_LAUNCHER__ from the environment as soon as it is no longer needed.

A more involved change would be to change both the interpreter and the stub executable to avoid the need to use an environment variable in the first place:

- Add and "-X" flag to the interpreter to pass the information that's currently passed using an environment variable
- Change pythonw.c to add this new option to the argv vector.

This would be slightly cleaner, at the cost of having more complicated code (and is a change that would IMHO not qualify for a back port, while my current PR is minimal enough for a back port)

Note that both with and without this PR sys.executable points to the python executable inside the venv (when using a env).