Hi,
I am dealing with the same issues.
what solved my errors was using python=3.7:
1.create and activate conda virtual environment
(conda create -n menpo-env python=3.7)
2. only installing menpo I was able using conda
(conda install -c conda-forge menpo)
BUT
when I tried installing other menpo packages I ran into conflicts again, so what I did instead was use (pip install)
so to sum up, if your only installing menpo then do:
(conda create -n menpo-env python=3.7)
(conda activate Menpo-env)
(conda install -c conda-forge menpo)
but if you want to install menpo, menpofit, menpodetect and menpo3d then do:
(conda create -n menpo-env python=3.7)
(conda activate Menpo-env)
(pip install menpo)
(pip install menpodetect)
(pip install menpofit)
(pip install menpo3d)
hope this helps:)