with winpython 2.2.20191022, we split the main process in 3:

• step1:
  . using Winpython 'builder' environment (not final WinPython):
  . we build a first basic WinPython structure with make.py, without installer creation, nor any package but pip/setuptools/wheel,
• step2:
  . moving inside WinPython target environment structure (the final WinPython),
  . pip install requirements.txt ,
  . run_complements.bat,
• step3:
  . moving back to Winpython 'builder' environment (not final WinPython):
  . we re-use make.py a second time to publish the build: remove_existing=False, no package addition nor run_requirement, just rebuilding changelog and creating installer

benefit:

• the goal: "run_complement.bat" step works again as expected on Python-3.8,
• FAIL: the Jupyterlab 32 bit re-build, inside "run_complement.bat" still doesn't work, jupyterlab-1.2.0a3 for https://github.com/jupyterlab/jupyterlab/pull/7201/files,
• make.py is unchanged,
• ... so it's the technical build simplification, without yet the code simplification.

cost:

• tweaking only "generate_a_winpython_distro.bat", not a technical big change
• rename run_complement.bat as run_complement_newbuild.bat

the problem it shall solve will remain not understood, so still lurking around: Win10, Python-3.8, ...