Instructions on download page (https://chirp.danplanet.com/projects/chirp/wiki/Download) for installing on macOS via brew do not currently work. The instructions say:
Homebrew users can install Chirp without the KK7DS runtime by running brew install tdsmith/ham/chirp and then running chirp from the terminal.
Running brew install tdsmith/ham/chirp
results in the following output:
brew install tdsmith/ham/chirp
Updating Homebrew...
==> Auto-updated Homebrew!
Updated Homebrew from 78140cef4 to ef12e329a.
Updated 3 taps (homebrew/core, homebrew/cask and homebrew/services).
...
It seems that pygtk has been removed from brew:
$brew search pygtk
No formula or cask found for "pygtk".