A really basic question...do you have graphviz itself installed? Looks like pymc doesn't require it for installation (see for instance https://docs.pymc.io/en/v3/api/model_graph.html)

%pip install graphviz

does it say that it's already installed? I had a similar issue in cython with using libgsl (I thought the package requiring it had installed it, but no)

edit: if anyone is coming here from google in the future. the solution above in itself isn't complete. pip only installs the python bindings for the graphviz executables (as detailed below). you'll still need to install graphviz either through apt or conda.

edit 2: if anyone is here from google in the future, your frustration in solving this problem is entirely valid and so are you 🙂 ... hopefully this solution works for your problem too.