The documentation page for the Standard Library, https://docs.python.org/3/library/, still says "Python 3.8.6 documentation" in the title. When visiting https://docs.python.org/3.9/library/ (emphasis on the 3.9) explicitly, the correct title is shown. I suspect there are other pages like this, perhaps ones that have not been modified since Python 3.8.6? This is possibly in fact some sort of bug in Sphinx, but I don't think so.