https://github.com/sphinx-toolbox/sphinx-toolbox-experimental there is no yet first release and sphinx-toolbox-experimental is not refistered on pypi.
It is a bit odd that released module is using another nit released yet module 😄
Is that modulerelally needed to build extras-require documentation?
If yes: are you going to make first release of the sphinx-toolbox-experimental and register it on pypi?