Fumbling with emacs + elpy + flake8

[Martin Schöön]

I am trying to set up emacs for Python coding on my secondary computer.
I follow these instructions but fail to make flake8 play with elpy:

https://realpython.com/emacs-the-best-python-editor/#elpy-python-development

I have done this some time in the past on my main computer and there it
works just fine. I have compared the set-up of this on the two computers
and fail to figure out why it works on one and not the other.

There are a couple of things that are not the same on the computers:

1) The secondary computer has a later version of emacs installed.

2) I used pip3 install --user flake8 on the secondary computer but on
the primary computer I think I left out the --user flag (not knowing
about it at the time) but I have added the path to .local/bin and
M-x elpy-config finds flake8 on both computers. Yet it does not
work on my secondary computer...

Any leads are greatly appreciated.

/Martin

PS Debian on both computers.