Trouble getting started with Eric and pyenv

[some.u...@posteo.net]

I have installed Eric in a virtual Env with pyenv and I need to have all my projects in own virtualenvs (to move them to other computers).
Using Ubuntu18.04, my  Eric20.5 does not see my installed packages. I see in the PyPI window a different list than on the command line. Programs using the standard library work fine in Eric. Programs that fail in Eric work fine on the command line. I ran out of ideas.

Here is what I did:
  sudo apt purge eric              # make sure the old stuff is fully gone
  pyenv install 3.6.9
  pyenv virtualenv 3.6.9 eric6
  pyenv activate eric6
  pip install eric-ide               # installs fine
  eric6                                     

Now for my simple projects I keep a common virtual env "default"
  pyenv virtualenv 3.6.9 default
   pyenv activate default             # works fine
   pip install wxPython               

Then I set "default" at Settings/Debugger/Python3 and both Run dialogs. When I open Eric's PyPI window and select "default" I see this:
   pip  18.1
   setuptools
On the CLI with pip list I get:
   pip  20.1                                   
   setuptools
   wxPython
   numpy
So somehow the "default" virtualevn Eric uses is something different that the "default" pyenv uses on the command line. I read that the pyenv approach with shims can cause difficulties, but I have seen answers in this archive that suggest others are using pyenv as well.  So I am hoping I have overlooked something.

Thanks
Tiger