we have just updated Sphinx (python-sphinx, python3-sphinx) to 3.1.1 in rawhide.
Packages that fail to build documentation with it have already been informed
weeks ago via Bugzilla.
CPython documentation cannot yet be built with Sphinx 3 and we will follow the
upstream development on this, eventually packaging Sphinx 2 to Fedora as well if
it will be needed.
Thanks for your patience when waiting for this.