What I tried:
brew install pygobject3 --with-python@2 gtk+3 brew install pygtk3 brew install pygobject3 pip install pygobject python -c \'import gi; gi.requ
install the gtk3 distribution version from Conda-forge channel
https://github.com/conda-forge/gtk3-feedstock/tree/cb80587f33166c0e19abe20ea7885a03bffda4ab