Comment 3 for bug 1914967

> my main system is Bionic which has python2 as default

There is not concept of "default" python in debian-based systems. the `python` command is python2, period.

> I changed that to python3 and [...]

That's not a supported setup. You get to keep the pieces.

the move from the unversioned /usr/bin/python to /usr/bin/python2 started years after bionic was released, so it's not surprising. In fact, back then using /usr/bin/python2 in shebangs was discouraged and partially automatically changed to the unversioned variant during the build.

I recommend you at least move to focal, even better groovy if you wish to have a /usr/bin/python pointing to python3. In there at least most packages will use /usr/bin/python2 in their shebang as you are describing. Either way, having /usr/bin/python pointing to python3 is not really supported by us at this time.