You should be doing this dynamically based on the version of python you are running against, so that you don't have to hardcode or make such "conservative" choices by hand.
But yes, if you have a Python version specified in pyproject.toml, we respect that, and if you have a virtualenv, we can see the Python version that was used to create that. And that's what we use to type-check your code.
The default being discussed here is what we fall back on if that project metadata isn't available.
IMO, a less presumptuous criticism would be phrased like "if you did X then benefits Y would happen", or "if you haven't, consider X", or even (the least presumptuous - make it a conversation!) "have you considered X?", rather than "you should do X".