[markrian]

You can install the [python-is-python3][0] package on 20.04, which symlinks /usr/bin/python to python3.

[0]: https://packages.ubuntu.com/focal/python-is-python3

[globular-toast]

I saw that, but it's not the default setting. You can't just write a python script and expect it to work on Ubuntu without putting python3 in the shebang.