Hi Jim,
I had a similar issue on Debian 10 the other day. It seems like components of the Python environment are not automatically kept up to date when simply running apt-get. So after running:
python3.7 -m pip install -U setuptools
... I also ran:
pip3 install --upgrade setuptools wheel pip3
Which then prepared the environment so I could run the nanovna-saver installer.
HTH
Marcel VK2CEL
