Netgen/NGSolve is written in C++17, which is not supported on MacOS 10.12 (at least 10.14 or 10.15 is needed)…
In case you cannot do a system upgrade for some reason, you may want to try older versions of NGSolve: https://www.asc.tuwien.ac.at//~mhochsteger/ngsolve/macos/
Note that older versions are also depending on older Python versions (3.6 or 3.7).
I was able to install ngsolve (older version: NGSolve-6.2.1901). But I have not problem in using the jupyter extension. When I use jupyter nbextension install --user --py ngsolve, I get the following error:
KeyError: ‘The Python module ngsolve is not a valid nbextension, it is missing the _jupyter_nbextension_paths() method.’
And when I trying to use: python3 -c ‘import ngsolve.webgui; ngsolve.webgui.howtoInstallJupyterLabextension()’
I am getting following error:
ModuleNotFoundError: No module named ‘ngsolve.webgui’