$ cmake .. -G Ninja -DCMAKE_INSTALL_PREFIX=/c/marshalnrn/nrn -DPYTHON_EXECUTABLE=/e/python39/python -DNRN_ENABLE_MPI_DYNAMIC=ON -DCMAKE_PREFIX_PATH="/c/ms-mpi" -DNRN_ENABLE_RX3D=OFF -DNRN_ENABLE_PYTHON_DYNAMIC=ON -DNRN_PYTHON_DYNAMIC="e:/python39/python"

CMake Error at external/iv/CMakeLists.txt:186 (add_subdirectory):
  add_subdirectory given source "src/lib" which is not an existing directory.

-- Looking for pthread.h
-- Looking for pthread.h - found

I did was launch python from the bash terminal and manually

from neuron import h, gui
g = h.Graph()
# in the Graph top left menu square select View/ObjectName and see if it prints Graph[0] to the terminal.
# also select Plotwhat? and cancel the poped up symbol chooser.
g.unmap() # should close the Graph
g.view(2) # should open it again
del g # should destroy it
# NEURONMainMenu/Build/CellBuilder should open a CellBuild[0]. Just Close it
makecellbuilder() # should open a CellBuild[0]. Click ContinuousCreate and a red checkmark should appear there.
h.topology() # should print something like `|-|       soma(0-1)`
# NEURONMainMenu/File/Quit to end the session.

sprint(nprocstr, "%d useful processors", np)