Thanks, working perfectly now. Somehow I was missing Cython from my command line. I used the command lines in your link and everything built fine.
I wonder if I could add a source to the sources list to avoid this in the future.
Unfortunately not, since this package has to be installed using pip (since python3 is required:
pip3), and not your local package manager.
But this command will update
all outdated pip packages:
pip3 list --outdated --format=freeze | grep -v '^\-e' | cut -d = -f 1 | xargs -n1 pip3 install -U
If you are running a server and need electrum to always work flawlessely you might consider adding this command to your cron file (which tells the server to execute a given script at a given time/interval).
I was running python updated already, but I didn't realize it couldn't be automated via a debian source list approach. I get it now.
Thanks to both of you members!!